tableam.h

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/*-------------------------------------------------------------------------
 *
 * tableam.h
 *    POSTGRES table access method definitions.
 *
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/tableam.h
 *
 * NOTES
 *      See tableam.sgml for higher level documentation.
 *
 *-------------------------------------------------------------------------
 */
#ifndef TABLEAM_H
#define TABLEAM_H
 
#include "access/relscan.h"
#include "access/sdir.h"
#include "access/xact.h"
#include "executor/tuptable.h"
#include "storage/read_stream.h"
#include "utils/rel.h"
#include "utils/snapshot.h"
 
 
#define DEFAULT_TABLE_ACCESS_METHOD "heap"
 
/* GUCs */
extern PGDLLIMPORT char *default_table_access_method;
extern PGDLLIMPORT bool synchronize_seqscans;
 
 
struct BulkInsertStateData;
struct IndexInfo;
struct SampleScanState;
struct VacuumParams;
struct ValidateIndexState;
 
/*
 * Bitmask values for the flags argument to the scan_begin callback.
 */
typedef enum ScanOptions
{
    /* one of SO_TYPE_* may be specified */
    SO_TYPE_SEQSCAN = 1 << 0,
    SO_TYPE_BITMAPSCAN = 1 << 1,
    SO_TYPE_SAMPLESCAN = 1 << 2,
    SO_TYPE_TIDSCAN = 1 << 3,
    SO_TYPE_TIDRANGESCAN = 1 << 4,
    SO_TYPE_ANALYZE = 1 << 5,
 
    /* several of SO_ALLOW_* may be specified */
    /* allow or disallow use of access strategy */
    SO_ALLOW_STRAT = 1 << 6,
    /* report location to syncscan logic? */
    SO_ALLOW_SYNC = 1 << 7,
    /* verify visibility page-at-a-time? */
    SO_ALLOW_PAGEMODE = 1 << 8,
 
    /* unregister snapshot at scan end? */
    SO_TEMP_SNAPSHOT = 1 << 9,
 
    /*
     * At the discretion of the table AM, bitmap table scans may be able to
     * skip fetching a block from the table if none of the table data is
     * needed. If table data may be needed, set SO_NEED_TUPLES.
     */
    SO_NEED_TUPLES = 1 << 10,
}           ScanOptions;
 
/*
 * Result codes for table_{update,delete,lock_tuple}, and for visibility
 * routines inside table AMs.
 */
typedef enum TM_Result
{
    /*
     * Signals that the action succeeded (i.e. update/delete performed, lock
     * was acquired)
     */
    TM_Ok,
 
    /* The affected tuple wasn't visible to the relevant snapshot */
    TM_Invisible,
 
    /* The affected tuple was already modified by the calling backend */
    TM_SelfModified,
 
    /*
     * The affected tuple was updated by another transaction. This includes
     * the case where tuple was moved to another partition.
     */
    TM_Updated,
 
    /* The affected tuple was deleted by another transaction */
    TM_Deleted,
 
    /*
     * The affected tuple is currently being modified by another session. This
     * will only be returned if table_(update/delete/lock_tuple) are
     * instructed not to wait.
     */
    TM_BeingModified,
 
    /* lock couldn't be acquired, action skipped. Only used by lock_tuple */
    TM_WouldBlock,
} TM_Result;
 
/*
 * Result codes for table_update(..., update_indexes*..).
 * Used to determine which indexes to update.
 */
typedef enum TU_UpdateIndexes
{
    /* No indexed columns were updated (incl. TID addressing of tuple) */
    TU_None,
 
    /* A non-summarizing indexed column was updated, or the TID has changed */
    TU_All,
 
    /* Only summarized columns were updated, TID is unchanged */
    TU_Summarizing,
} TU_UpdateIndexes;
 
/*
 * When table_tuple_update, table_tuple_delete, or table_tuple_lock fail
 * because the target tuple is already outdated, they fill in this struct to
 * provide information to the caller about what happened.
 *
 * ctid is the target's ctid link: it is the same as the target's TID if the
 * target was deleted, or the location of the replacement tuple if the target
 * was updated.
 *
 * xmax is the outdating transaction's XID.  If the caller wants to visit the
 * replacement tuple, it must check that this matches before believing the
 * replacement is really a match.
 *
 * cmax is the outdating command's CID, but only when the failure code is
 * TM_SelfModified (i.e., something in the current transaction outdated the
 * tuple); otherwise cmax is zero.  (We make this restriction because
 * HeapTupleHeaderGetCmax doesn't work for tuples outdated in other
 * transactions.)
 */
typedef struct TM_FailureData
{
    ItemPointerData ctid;
    TransactionId xmax;
    CommandId   cmax;
    bool        traversed;
} TM_FailureData;
 
/*
 * State used when calling table_index_delete_tuples().
 *
 * Represents the status of table tuples, referenced by table TID and taken by
 * index AM from index tuples.  State consists of high level parameters of the
 * deletion operation, plus two mutable palloc()'d arrays for information
 * about the status of individual table tuples.  These are conceptually one
 * single array.  Using two arrays keeps the TM_IndexDelete struct small,
 * which makes sorting the first array (the deltids array) fast.
 *
 * Some index AM callers perform simple index tuple deletion (by specifying
 * bottomup = false), and include only known-dead deltids.  These known-dead
 * entries are all marked knowndeletable = true directly (typically these are
 * TIDs from LP_DEAD-marked index tuples), but that isn't strictly required.
 *
 * Callers that specify bottomup = true are "bottom-up index deletion"
 * callers.  The considerations for the tableam are more subtle with these
 * callers because they ask the tableam to perform highly speculative work,
 * and might only expect the tableam to check a small fraction of all entries.
 * Caller is not allowed to specify knowndeletable = true for any entry
 * because everything is highly speculative.  Bottom-up caller provides
 * context and hints to tableam -- see comments below for details on how index
 * AMs and tableams should coordinate during bottom-up index deletion.
 *
 * Simple index deletion callers may ask the tableam to perform speculative
 * work, too.  This is a little like bottom-up deletion, but not too much.
 * The tableam will only perform speculative work when it's practically free
 * to do so in passing for simple deletion caller (while always performing
 * whatever work is needed to enable knowndeletable/LP_DEAD index tuples to
 * be deleted within index AM).  This is the real reason why it's possible for
 * simple index deletion caller to specify knowndeletable = false up front
 * (this means "check if it's possible for me to delete corresponding index
 * tuple when it's cheap to do so in passing").  The index AM should only
 * include "extra" entries for index tuples whose TIDs point to a table block
 * that tableam is expected to have to visit anyway (in the event of a block
 * orientated tableam).  The tableam isn't strictly obligated to check these
 * "extra" TIDs, but a block-based AM should always manage to do so in
 * practice.
 *
 * The final contents of the deltids/status arrays are interesting to callers
 * that ask tableam to perform speculative work (i.e. when _any_ items have
 * knowndeletable set to false up front).  These index AM callers will
 * naturally need to consult final state to determine which index tuples are
 * in fact deletable.
 *
 * The index AM can keep track of which index tuple relates to which deltid by
 * setting idxoffnum (and/or relying on each entry being uniquely identifiable
 * using tid), which is important when the final contents of the array will
 * need to be interpreted -- the array can shrink from initial size after
 * tableam processing and/or have entries in a new order (tableam may sort
 * deltids array for its own reasons).  Bottom-up callers may find that final
 * ndeltids is 0 on return from call to tableam, in which case no index tuple
 * deletions are possible.  Simple deletion callers can rely on any entries
 * they know to be deletable appearing in the final array as deletable.
 */
typedef struct TM_IndexDelete
{
    ItemPointerData tid;        /* table TID from index tuple */
    int16       id;             /* Offset into TM_IndexStatus array */
} TM_IndexDelete;
 
typedef struct TM_IndexStatus
{
    OffsetNumber idxoffnum;     /* Index am page offset number */
    bool        knowndeletable; /* Currently known to be deletable? */
 
    /* Bottom-up index deletion specific fields follow */
    bool        promising;      /* Promising (duplicate) index tuple? */
    int16       freespace;      /* Space freed in index if deleted */
} TM_IndexStatus;
 
/*
 * Index AM/tableam coordination is central to the design of bottom-up index
 * deletion.  The index AM provides hints about where to look to the tableam
 * by marking some entries as "promising".  Index AM does this with duplicate
 * index tuples that are strongly suspected to be old versions left behind by
 * UPDATEs that did not logically modify indexed values.  Index AM may find it
 * helpful to only mark entries as promising when they're thought to have been
 * affected by such an UPDATE in the recent past.
 *
 * Bottom-up index deletion casts a wide net at first, usually by including
 * all TIDs on a target index page.  It is up to the tableam to worry about
 * the cost of checking transaction status information.  The tableam is in
 * control, but needs careful guidance from the index AM.  Index AM requests
 * that bottomupfreespace target be met, while tableam measures progress
 * towards that goal by tallying the per-entry freespace value for known
 * deletable entries. (All !bottomup callers can just set these space related
 * fields to zero.)
 */
typedef struct TM_IndexDeleteOp
{
    Relation    irel;           /* Target index relation */
    BlockNumber iblknum;        /* Index block number (for error reports) */
    bool        bottomup;       /* Bottom-up (not simple) deletion? */
    int         bottomupfreespace;  /* Bottom-up space target */
 
    /* Mutable per-TID information follows (index AM initializes entries) */
    int         ndeltids;       /* Current # of deltids/status elements */
    TM_IndexDelete *deltids;
    TM_IndexStatus *status;
} TM_IndexDeleteOp;
 
/* "options" flag bits for table_tuple_insert */
/* TABLE_INSERT_SKIP_WAL was 0x0001; RelationNeedsWAL() now governs */
#define TABLE_INSERT_SKIP_FSM       0x0002
#define TABLE_INSERT_FROZEN         0x0004
#define TABLE_INSERT_NO_LOGICAL     0x0008
 
/* flag bits for table_tuple_lock */
/* Follow tuples whose update is in progress if lock modes don't conflict  */
#define TUPLE_LOCK_FLAG_LOCK_UPDATE_IN_PROGRESS (1 << 0)
/* Follow update chain and lock latest version of tuple */
#define TUPLE_LOCK_FLAG_FIND_LAST_VERSION       (1 << 1)
 
 
/* Typedef for callback function for table_index_build_scan */
typedef void (*IndexBuildCallback) (Relation index,
                                    ItemPointer tid,
                                    Datum *values,
                                    bool *isnull,
                                    bool tupleIsAlive,
                                    void *state);
 
/*
 * API struct for a table AM.  Note this must be allocated in a
 * server-lifetime manner, typically as a static const struct, which then gets
 * returned by FormData_pg_am.amhandler.
 *
 * In most cases it's not appropriate to call the callbacks directly, use the
 * table_* wrapper functions instead.
 *
 * GetTableAmRoutine() asserts that required callbacks are filled in, remember
 * to update when adding a callback.
 */
typedef struct TableAmRoutine
{
    /* this must be set to T_TableAmRoutine */
    NodeTag     type;
 
 
    /* ------------------------------------------------------------------------
     * Slot related callbacks.
     * ------------------------------------------------------------------------
     */
 
    /*
     * Return slot implementation suitable for storing a tuple of this AM.
     */
    const TupleTableSlotOps *(*slot_callbacks) (Relation rel);
 
 
    /* ------------------------------------------------------------------------
     * Table scan callbacks.
     * ------------------------------------------------------------------------
     */
 
    /*
     * Start a scan of `rel`.  The callback has to return a TableScanDesc,
     * which will typically be embedded in a larger, AM specific, struct.
     *
     * If nkeys != 0, the results need to be filtered by those scan keys.
     *
     * pscan, if not NULL, will have already been initialized with
     * parallelscan_initialize(), and has to be for the same relation. Will
     * only be set coming from table_beginscan_parallel().
     *
     * `flags` is a bitmask indicating the type of scan (ScanOptions's
     * SO_TYPE_*, currently only one may be specified), options controlling
     * the scan's behaviour (ScanOptions's SO_ALLOW_*, several may be
     * specified, an AM may ignore unsupported ones) and whether the snapshot
     * needs to be deallocated at scan_end (ScanOptions's SO_TEMP_SNAPSHOT).
     */
    TableScanDesc (*scan_begin) (Relation rel,
                                 Snapshot snapshot,
                                 int nkeys, struct ScanKeyData *key,
                                 ParallelTableScanDesc pscan,
                                 uint32 flags);
 
    /*
     * Release resources and deallocate scan. If TableScanDesc.temp_snap,
     * TableScanDesc.rs_snapshot needs to be unregistered.
     */
    void        (*scan_end) (TableScanDesc scan);
 
    /*
     * Restart relation scan.  If set_params is set to true, allow_{strat,
     * sync, pagemode} (see scan_begin) changes should be taken into account.
     */
    void        (*scan_rescan) (TableScanDesc scan, struct ScanKeyData *key,
                                bool set_params, bool allow_strat,
                                bool allow_sync, bool allow_pagemode);
 
    /*
     * Return next tuple from `scan`, store in slot.
     */
    bool        (*scan_getnextslot) (TableScanDesc scan,
                                     ScanDirection direction,
                                     TupleTableSlot *slot);
 
    /*-----------
     * Optional functions to provide scanning for ranges of ItemPointers.
     * Implementations must either provide both of these functions, or neither
     * of them.
     *
     * Implementations of scan_set_tidrange must themselves handle
     * ItemPointers of any value. i.e, they must handle each of the following:
     *
     * 1) mintid or maxtid is beyond the end of the table; and
     * 2) mintid is above maxtid; and
     * 3) item offset for mintid or maxtid is beyond the maximum offset
     * allowed by the AM.
     *
     * Implementations can assume that scan_set_tidrange is always called
     * before scan_getnextslot_tidrange or after scan_rescan and before any
     * further calls to scan_getnextslot_tidrange.
     */
    void        (*scan_set_tidrange) (TableScanDesc scan,
                                      ItemPointer mintid,
                                      ItemPointer maxtid);
 
    /*
     * Return next tuple from `scan` that's in the range of TIDs defined by
     * scan_set_tidrange.
     */
    bool        (*scan_getnextslot_tidrange) (TableScanDesc scan,
                                              ScanDirection direction,
                                              TupleTableSlot *slot);
 
    /* ------------------------------------------------------------------------
     * Parallel table scan related functions.
     * ------------------------------------------------------------------------
     */
 
    /*
     * Estimate the size of shared memory needed for a parallel scan of this
     * relation. The snapshot does not need to be accounted for.
     */
    Size        (*parallelscan_estimate) (Relation rel);
 
    /*
     * Initialize ParallelTableScanDesc for a parallel scan of this relation.
     * `pscan` will be sized according to parallelscan_estimate() for the same
     * relation.
     */
    Size        (*parallelscan_initialize) (Relation rel,
                                            ParallelTableScanDesc pscan);
 
    /*
     * Reinitialize `pscan` for a new scan. `rel` will be the same relation as
     * when `pscan` was initialized by parallelscan_initialize.
     */
    void        (*parallelscan_reinitialize) (Relation rel,
                                              ParallelTableScanDesc pscan);
 
 
    /* ------------------------------------------------------------------------
     * Index Scan Callbacks
     * ------------------------------------------------------------------------
     */
 
    /*
     * Prepare to fetch tuples from the relation, as needed when fetching
     * tuples for an index scan.  The callback has to return an
     * IndexFetchTableData, which the AM will typically embed in a larger
     * structure with additional information.
     *
     * Tuples for an index scan can then be fetched via index_fetch_tuple.
     */
    struct IndexFetchTableData *(*index_fetch_begin) (Relation rel);
 
    /*
     * Reset index fetch. Typically this will release cross index fetch
     * resources held in IndexFetchTableData.
     */
    void        (*index_fetch_reset) (struct IndexFetchTableData *data);
 
    /*
     * Release resources and deallocate index fetch.
     */
    void        (*index_fetch_end) (struct IndexFetchTableData *data);
 
    /*
     * Fetch tuple at `tid` into `slot`, after doing a visibility test
     * according to `snapshot`. If a tuple was found and passed the visibility
     * test, return true, false otherwise.
     *
     * Note that AMs that do not necessarily update indexes when indexed
     * columns do not change, need to return the current/correct version of
     * the tuple that is visible to the snapshot, even if the tid points to an
     * older version of the tuple.
     *
     * *call_again is false on the first call to index_fetch_tuple for a tid.
     * If there potentially is another tuple matching the tid, *call_again
     * needs to be set to true by index_fetch_tuple, signaling to the caller
     * that index_fetch_tuple should be called again for the same tid.
     *
     * *all_dead, if all_dead is not NULL, should be set to true by
     * index_fetch_tuple iff it is guaranteed that no backend needs to see
     * that tuple. Index AMs can use that to avoid returning that tid in
     * future searches.
     */
    bool        (*index_fetch_tuple) (struct IndexFetchTableData *scan,
                                      ItemPointer tid,
                                      Snapshot snapshot,
                                      TupleTableSlot *slot,
                                      bool *call_again, bool *all_dead);
 
 
    /* ------------------------------------------------------------------------
     * Callbacks for non-modifying operations on individual tuples
     * ------------------------------------------------------------------------
     */
 
    /*
     * Fetch tuple at `tid` into `slot`, after doing a visibility test
     * according to `snapshot`. If a tuple was found and passed the visibility
     * test, returns true, false otherwise.
     */
    bool        (*tuple_fetch_row_version) (Relation rel,
                                            ItemPointer tid,
                                            Snapshot snapshot,
                                            TupleTableSlot *slot);
 
    /*
     * Is tid valid for a scan of this relation.
     */
    bool        (*tuple_tid_valid) (TableScanDesc scan,
                                    ItemPointer tid);
 
    /*
     * Return the latest version of the tuple at `tid`, by updating `tid` to
     * point at the newest version.
     */
    void        (*tuple_get_latest_tid) (TableScanDesc scan,
                                         ItemPointer tid);
 
    /*
     * Does the tuple in `slot` satisfy `snapshot`?  The slot needs to be of
     * the appropriate type for the AM.
     */
    bool        (*tuple_satisfies_snapshot) (Relation rel,
                                             TupleTableSlot *slot,
                                             Snapshot snapshot);
 
    /* see table_index_delete_tuples() */
    TransactionId (*index_delete_tuples) (Relation rel,
                                          TM_IndexDeleteOp *delstate);
 
 
    /* ------------------------------------------------------------------------
     * Manipulations of physical tuples.
     * ------------------------------------------------------------------------
     */
 
    /* see table_tuple_insert() for reference about parameters */
    void        (*tuple_insert) (Relation rel, TupleTableSlot *slot,
                                 CommandId cid, int options,
                                 struct BulkInsertStateData *bistate);
 
    /* see table_tuple_insert_speculative() for reference about parameters */
    void        (*tuple_insert_speculative) (Relation rel,
                                             TupleTableSlot *slot,
                                             CommandId cid,
                                             int options,
                                             struct BulkInsertStateData *bistate,
                                             uint32 specToken);
 
    /* see table_tuple_complete_speculative() for reference about parameters */
    void        (*tuple_complete_speculative) (Relation rel,
                                               TupleTableSlot *slot,
                                               uint32 specToken,
                                               bool succeeded);
 
    /* see table_multi_insert() for reference about parameters */
    void        (*multi_insert) (Relation rel, TupleTableSlot **slots, int nslots,
                                 CommandId cid, int options, struct BulkInsertStateData *bistate);
 
    /* see table_tuple_delete() for reference about parameters */
    TM_Result   (*tuple_delete) (Relation rel,
                                 ItemPointer tid,
                                 CommandId cid,
                                 Snapshot snapshot,
                                 Snapshot crosscheck,
                                 bool wait,
                                 TM_FailureData *tmfd,
                                 bool changingPart);
 
    /* see table_tuple_update() for reference about parameters */
    TM_Result   (*tuple_update) (Relation rel,
                                 ItemPointer otid,
                                 TupleTableSlot *slot,
                                 CommandId cid,
                                 Snapshot snapshot,
                                 Snapshot crosscheck,
                                 bool wait,
                                 TM_FailureData *tmfd,
                                 LockTupleMode *lockmode,
                                 TU_UpdateIndexes *update_indexes);
 
    /* see table_tuple_lock() for reference about parameters */
    TM_Result   (*tuple_lock) (Relation rel,
                               ItemPointer tid,
                               Snapshot snapshot,
                               TupleTableSlot *slot,
                               CommandId cid,
                               LockTupleMode mode,
                               LockWaitPolicy wait_policy,
                               uint8 flags,
                               TM_FailureData *tmfd);
 
    /*
     * Perform operations necessary to complete insertions made via
     * tuple_insert and multi_insert with a BulkInsertState specified. In-tree
     * access methods ceased to use this.
     *
     * Typically callers of tuple_insert and multi_insert will just pass all
     * the flags that apply to them, and each AM has to decide which of them
     * make sense for it, and then only take actions in finish_bulk_insert for
     * those flags, and ignore others.
     *
     * Optional callback.
     */
    void        (*finish_bulk_insert) (Relation rel, int options);
 
 
    /* ------------------------------------------------------------------------
     * DDL related functionality.
     * ------------------------------------------------------------------------
     */
 
    /*
     * This callback needs to create new relation storage for `rel`, with
     * appropriate durability behaviour for `persistence`.
     *
     * Note that only the subset of the relcache filled by
     * RelationBuildLocalRelation() can be relied upon and that the relation's
     * catalog entries will either not yet exist (new relation), or will still
     * reference the old relfilelocator.
     *
     * As output *freezeXid, *minmulti must be set to the values appropriate
     * for pg_class.{relfrozenxid, relminmxid}. For AMs that don't need those
     * fields to be filled they can be set to InvalidTransactionId and
     * InvalidMultiXactId, respectively.
     *
     * See also table_relation_set_new_filelocator().
     */
    void        (*relation_set_new_filelocator) (Relation rel,
                                                 const RelFileLocator *newrlocator,
                                                 char persistence,
                                                 TransactionId *freezeXid,
                                                 MultiXactId *minmulti);
 
    /*
     * This callback needs to remove all contents from `rel`'s current
     * relfilelocator. No provisions for transactional behaviour need to be
     * made.  Often this can be implemented by truncating the underlying
     * storage to its minimal size.
     *
     * See also table_relation_nontransactional_truncate().
     */
    void        (*relation_nontransactional_truncate) (Relation rel);
 
    /*
     * See table_relation_copy_data().
     *
     * This can typically be implemented by directly copying the underlying
     * storage, unless it contains references to the tablespace internally.
     */
    void        (*relation_copy_data) (Relation rel,
                                       const RelFileLocator *newrlocator);
 
    /* See table_relation_copy_for_cluster() */
    void        (*relation_copy_for_cluster) (Relation OldTable,
                                              Relation NewTable,
                                              Relation OldIndex,
                                              bool use_sort,
                                              TransactionId OldestXmin,
                                              TransactionId *xid_cutoff,
                                              MultiXactId *multi_cutoff,
                                              double *num_tuples,
                                              double *tups_vacuumed,
                                              double *tups_recently_dead);
 
    /*
     * React to VACUUM command on the relation. The VACUUM can be triggered by
     * a user or by autovacuum. The specific actions performed by the AM will
     * depend heavily on the individual AM.
     *
     * On entry a transaction is already established, and the relation is
     * locked with a ShareUpdateExclusive lock.
     *
     * Note that neither VACUUM FULL (and CLUSTER), nor ANALYZE go through
     * this routine, even if (for ANALYZE) it is part of the same VACUUM
     * command.
     *
     * There probably, in the future, needs to be a separate callback to
     * integrate with autovacuum's scheduling.
     */
    void        (*relation_vacuum) (Relation rel,
                                    struct VacuumParams *params,
                                    BufferAccessStrategy bstrategy);
 
    /*
     * Prepare to analyze block `blockno` of `scan`. The scan has been started
     * with table_beginscan_analyze().  See also
     * table_scan_analyze_next_block().
     *
     * The callback may acquire resources like locks that are held until
     * table_scan_analyze_next_tuple() returns false. It e.g. can make sense
     * to hold a lock until all tuples on a block have been analyzed by
     * scan_analyze_next_tuple.
     *
     * The callback can return false if the block is not suitable for
     * sampling, e.g. because it's a metapage that could never contain tuples.
     *
     * XXX: This obviously is primarily suited for block-based AMs. It's not
     * clear what a good interface for non block based AMs would be, so there
     * isn't one yet.
     */
    bool        (*scan_analyze_next_block) (TableScanDesc scan,
                                            ReadStream *stream);
 
    /*
     * See table_scan_analyze_next_tuple().
     *
     * Not every AM might have a meaningful concept of dead rows, in which
     * case it's OK to not increment *deadrows - but note that that may
     * influence autovacuum scheduling (see comment for relation_vacuum
     * callback).
     */
    bool        (*scan_analyze_next_tuple) (TableScanDesc scan,
                                            TransactionId OldestXmin,
                                            double *liverows,
                                            double *deadrows,
                                            TupleTableSlot *slot);
 
    /* see table_index_build_range_scan for reference about parameters */
    double      (*index_build_range_scan) (Relation table_rel,
                                           Relation index_rel,
                                           struct IndexInfo *index_info,
                                           bool allow_sync,
                                           bool anyvisible,
                                           bool progress,
                                           BlockNumber start_blockno,
                                           BlockNumber numblocks,
                                           IndexBuildCallback callback,
                                           void *callback_state,
                                           TableScanDesc scan);
 
    /* see table_index_validate_scan for reference about parameters */
    void        (*index_validate_scan) (Relation table_rel,
                                        Relation index_rel,
                                        struct IndexInfo *index_info,
                                        Snapshot snapshot,
                                        struct ValidateIndexState *state);
 
 
    /* ------------------------------------------------------------------------
     * Miscellaneous functions.
     * ------------------------------------------------------------------------
     */
 
    /*
     * See table_relation_size().
     *
     * Note that currently a few callers use the MAIN_FORKNUM size to figure
     * out the range of potentially interesting blocks (brin, analyze). It's
     * probable that we'll need to revise the interface for those at some
     * point.
     */
    uint64      (*relation_size) (Relation rel, ForkNumber forkNumber);
 
 
    /*
     * This callback should return true if the relation requires a TOAST table
     * and false if it does not.  It may wish to examine the relation's tuple
     * descriptor before making a decision, but if it uses some other method
     * of storing large values (or if it does not support them) it can simply
     * return false.
     */
    bool        (*relation_needs_toast_table) (Relation rel);
 
    /*
     * This callback should return the OID of the table AM that implements
     * TOAST tables for this AM.  If the relation_needs_toast_table callback
     * always returns false, this callback is not required.
     */
    Oid         (*relation_toast_am) (Relation rel);
 
    /*
     * This callback is invoked when detoasting a value stored in a toast
     * table implemented by this AM.  See table_relation_fetch_toast_slice()
     * for more details.
     */
    void        (*relation_fetch_toast_slice) (Relation toastrel, Oid valueid,
                                               int32 attrsize,
                                               int32 sliceoffset,
                                               int32 slicelength,
                                               struct varlena *result);
 
 
    /* ------------------------------------------------------------------------
     * Planner related functions.
     * ------------------------------------------------------------------------
     */
 
    /*
     * See table_relation_estimate_size().
     *
     * While block oriented, it shouldn't be too hard for an AM that doesn't
     * internally use blocks to convert into a usable representation.
     *
     * This differs from the relation_size callback by returning size
     * estimates (both relation size and tuple count) for planning purposes,
     * rather than returning a currently correct estimate.
     */
    void        (*relation_estimate_size) (Relation rel, int32 *attr_widths,
                                           BlockNumber *pages, double *tuples,
                                           double *allvisfrac);
 
 
    /* ------------------------------------------------------------------------
     * Executor related functions.
     * ------------------------------------------------------------------------
     */
 
    /*
     * Prepare to fetch / check / return tuples from `blockno` as part of a
     * bitmap table scan. `scan` was started via table_beginscan_bm(). Return
     * false if the bitmap is exhausted and true otherwise.
     *
     * This will typically read and pin the target block, and do the necessary
     * work to allow scan_bitmap_next_tuple() to return tuples (e.g. it might
     * make sense to perform tuple visibility checks at this time).
     *
     * `lossy_pages` and `exact_pages` are EXPLAIN counters that can be
     * incremented by the table AM to indicate whether or not the block's
     * representation in the bitmap is lossy.
     *
     * `recheck` is set by the table AM to indicate whether or not the tuples
     * from this block should be rechecked. Tuples from lossy pages will
     * always need to be rechecked, but some non-lossy pages' tuples may also
     * require recheck.
     *
     * `blockno` is the current block and is set by the table AM. The table AM
     * is responsible for advancing the main iterator, but the bitmap table
     * scan code still advances the prefetch iterator. `blockno` is used by
     * bitmap table scan code to validate that the prefetch block stays ahead
     * of the current block.
     *
     * XXX: Currently this may only be implemented if the AM uses md.c as its
     * storage manager, and uses ItemPointer->ip_blkid in a manner that maps
     * blockids directly to the underlying storage. nodeBitmapHeapscan.c
     * performs prefetching directly using that interface.  This probably
     * needs to be rectified at a later point.
     *
     * XXX: Currently this may only be implemented if the AM uses the
     * visibilitymap, as nodeBitmapHeapscan.c unconditionally accesses it to
     * perform prefetching.  This probably needs to be rectified at a later
     * point.
     *
     * Optional callback, but either both scan_bitmap_next_block and
     * scan_bitmap_next_tuple need to exist, or neither.
     */
    bool        (*scan_bitmap_next_block) (TableScanDesc scan,
                                           BlockNumber *blockno,
                                           bool *recheck,
                                           uint64 *lossy_pages,
                                           uint64 *exact_pages);
 
    /*
     * Fetch the next tuple of a bitmap table scan into `slot` and return true
     * if a visible tuple was found, false otherwise.
     *
     * Optional callback, but either both scan_bitmap_next_block and
     * scan_bitmap_next_tuple need to exist, or neither.
     */
    bool        (*scan_bitmap_next_tuple) (TableScanDesc scan,
                                           TupleTableSlot *slot);
 
    /*
     * Prepare to fetch tuples from the next block in a sample scan. Return
     * false if the sample scan is finished, true otherwise. `scan` was
     * started via table_beginscan_sampling().
     *
     * Typically this will first determine the target block by calling the
     * TsmRoutine's NextSampleBlock() callback if not NULL, or alternatively
     * perform a sequential scan over all blocks.  The determined block is
     * then typically read and pinned.
     *
     * As the TsmRoutine interface is block based, a block needs to be passed
     * to NextSampleBlock(). If that's not appropriate for an AM, it
     * internally needs to perform mapping between the internal and a block
     * based representation.
     *
     * Note that it's not acceptable to hold deadlock prone resources such as
     * lwlocks until scan_sample_next_tuple() has exhausted the tuples on the
     * block - the tuple is likely to be returned to an upper query node, and
     * the next call could be off a long while. Holding buffer pins and such
     * is obviously OK.
     *
     * Currently it is required to implement this interface, as there's no
     * alternative way (contrary e.g. to bitmap scans) to implement sample
     * scans. If infeasible to implement, the AM may raise an error.
     */
    bool        (*scan_sample_next_block) (TableScanDesc scan,
                                           struct SampleScanState *scanstate);
 
    /*
     * This callback, only called after scan_sample_next_block has returned
     * true, should determine the next tuple to be returned from the selected
     * block using the TsmRoutine's NextSampleTuple() callback.
     *
     * The callback needs to perform visibility checks, and only return
     * visible tuples. That obviously can mean calling NextSampleTuple()
     * multiple times.
     *
     * The TsmRoutine interface assumes that there's a maximum offset on a
     * given page, so if that doesn't apply to an AM, it needs to emulate that
     * assumption somehow.
     */
    bool        (*scan_sample_next_tuple) (TableScanDesc scan,
                                           struct SampleScanState *scanstate,
                                           TupleTableSlot *slot);
 
} TableAmRoutine;
 
 
/* ----------------------------------------------------------------------------
 * Slot functions.
 * ----------------------------------------------------------------------------
 */
 
/*
 * Returns slot callbacks suitable for holding tuples of the appropriate type
 * for the relation.  Works for tables, views, foreign tables and partitioned
 * tables.
 */
extern const TupleTableSlotOps *table_slot_callbacks(Relation relation);
 
/*
 * Returns slot using the callbacks returned by table_slot_callbacks(), and
 * registers it on *reglist.
 */
extern TupleTableSlot *table_slot_create(Relation relation, List **reglist);
 
 
/* ----------------------------------------------------------------------------
 * Table scan functions.
 * ----------------------------------------------------------------------------
 */
 
/*
 * Start a scan of `rel`. Returned tuples pass a visibility test of
 * `snapshot`, and if nkeys != 0, the results are filtered by those scan keys.
 */
static inline TableScanDesc
table_beginscan(Relation rel, Snapshot snapshot,
                int nkeys, struct ScanKeyData *key)
{
    uint32      flags = SO_TYPE_SEQSCAN |
        SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE;
 
    return rel->rd_tableam->scan_begin(rel, snapshot, nkeys, key, NULL, flags);
}
 
/*
 * Like table_beginscan(), but for scanning catalog. It'll automatically use a
 * snapshot appropriate for scanning catalog relations.
 */
extern TableScanDesc table_beginscan_catalog(Relation relation, int nkeys,
                                             struct ScanKeyData *key);
 
/*
 * Like table_beginscan(), but table_beginscan_strat() offers an extended API
 * that lets the caller control whether a nondefault buffer access strategy
 * can be used, and whether syncscan can be chosen (possibly resulting in the
 * scan not starting from block zero).  Both of these default to true with
 * plain table_beginscan.
 */
static inline TableScanDesc
table_beginscan_strat(Relation rel, Snapshot snapshot,
                      int nkeys, struct ScanKeyData *key,
                      bool allow_strat, bool allow_sync)
{
    uint32      flags = SO_TYPE_SEQSCAN | SO_ALLOW_PAGEMODE;
 
    if (allow_strat)
        flags |= SO_ALLOW_STRAT;
    if (allow_sync)
        flags |= SO_ALLOW_SYNC;
 
    return rel->rd_tableam->scan_begin(rel, snapshot, nkeys, key, NULL, flags);
}
 
/*
 * table_beginscan_bm is an alternative entry point for setting up a
 * TableScanDesc for a bitmap heap scan.  Although that scan technology is
 * really quite unlike a standard seqscan, there is just enough commonality to
 * make it worth using the same data structure.
 */
static inline TableScanDesc
table_beginscan_bm(Relation rel, Snapshot snapshot,
                   int nkeys, struct ScanKeyData *key, bool need_tuple)
{
    TableScanDesc result;
    uint32      flags = SO_TYPE_BITMAPSCAN | SO_ALLOW_PAGEMODE;
 
    if (need_tuple)
        flags |= SO_NEED_TUPLES;
 
    result = rel->rd_tableam->scan_begin(rel, snapshot, nkeys, key,
                                         NULL, flags);
    result->st.bitmap.rs_shared_iterator = NULL;
    result->st.bitmap.rs_iterator = NULL;
    return result;
}
 
/*
 * table_beginscan_sampling is an alternative entry point for setting up a
 * TableScanDesc for a TABLESAMPLE scan.  As with bitmap scans, it's worth
 * using the same data structure although the behavior is rather different.
 * In addition to the options offered by table_beginscan_strat, this call
 * also allows control of whether page-mode visibility checking is used.
 */
static inline TableScanDesc
table_beginscan_sampling(Relation rel, Snapshot snapshot,
                         int nkeys, struct ScanKeyData *key,
                         bool allow_strat, bool allow_sync,
                         bool allow_pagemode)
{
    uint32      flags = SO_TYPE_SAMPLESCAN;
 
    if (allow_strat)
        flags |= SO_ALLOW_STRAT;
    if (allow_sync)
        flags |= SO_ALLOW_SYNC;
    if (allow_pagemode)
        flags |= SO_ALLOW_PAGEMODE;
 
    return rel->rd_tableam->scan_begin(rel, snapshot, nkeys, key, NULL, flags);
}
 
/*
 * table_beginscan_tid is an alternative entry point for setting up a
 * TableScanDesc for a Tid scan. As with bitmap scans, it's worth using
 * the same data structure although the behavior is rather different.
 */
static inline TableScanDesc
table_beginscan_tid(Relation rel, Snapshot snapshot)
{
    uint32      flags = SO_TYPE_TIDSCAN;
 
    return rel->rd_tableam->scan_begin(rel, snapshot, 0, NULL, NULL, flags);
}
 
/*
 * table_beginscan_analyze is an alternative entry point for setting up a
 * TableScanDesc for an ANALYZE scan.  As with bitmap scans, it's worth using
 * the same data structure although the behavior is rather different.
 */
static inline TableScanDesc
table_beginscan_analyze(Relation rel)
{
    uint32      flags = SO_TYPE_ANALYZE;
 
    return rel->rd_tableam->scan_begin(rel, NULL, 0, NULL, NULL, flags);
}
 
/*
 * End relation scan.
 */
static inline void
table_endscan(TableScanDesc scan)
{
    scan->rs_rd->rd_tableam->scan_end(scan);
}
 
/*
 * Restart a relation scan.
 */
static inline void
table_rescan(TableScanDesc scan,
             struct ScanKeyData *key)
{
    scan->rs_rd->rd_tableam->scan_rescan(scan, key, false, false, false, false);
}
 
/*
 * Restart a relation scan after changing params.
 *
 * This call allows changing the buffer strategy, syncscan, and pagemode
 * options before starting a fresh scan.  Note that although the actual use of
 * syncscan might change (effectively, enabling or disabling reporting), the
 * previously selected startblock will be kept.
 */
static inline void
table_rescan_set_params(TableScanDesc scan, struct ScanKeyData *key,
                        bool allow_strat, bool allow_sync, bool allow_pagemode)
{
    scan->rs_rd->rd_tableam->scan_rescan(scan, key, true,
                                         allow_strat, allow_sync,
                                         allow_pagemode);
}
 
/*
 * Return next tuple from `scan`, store in slot.
 */
static inline bool
table_scan_getnextslot(TableScanDesc sscan, ScanDirection direction, TupleTableSlot *slot)
{
    slot->tts_tableOid = RelationGetRelid(sscan->rs_rd);
 
    /* We don't expect actual scans using NoMovementScanDirection */
    Assert(direction == ForwardScanDirection ||
           direction == BackwardScanDirection);
 
    /*
     * We don't expect direct calls to table_scan_getnextslot with valid
     * CheckXidAlive for catalog or regular tables.  See detailed comments in
     * xact.c where these variables are declared.
     */
    if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
        elog(ERROR, "unexpected table_scan_getnextslot call during logical decoding");
 
    return sscan->rs_rd->rd_tableam->scan_getnextslot(sscan, direction, slot);
}
 
/* ----------------------------------------------------------------------------
 * TID Range scanning related functions.
 * ----------------------------------------------------------------------------
 */
 
/*
 * table_beginscan_tidrange is the entry point for setting up a TableScanDesc
 * for a TID range scan.
 */
static inline TableScanDesc
table_beginscan_tidrange(Relation rel, Snapshot snapshot,
                         ItemPointer mintid,
                         ItemPointer maxtid)
{
    TableScanDesc sscan;
    uint32      flags = SO_TYPE_TIDRANGESCAN | SO_ALLOW_PAGEMODE;
 
    sscan = rel->rd_tableam->scan_begin(rel, snapshot, 0, NULL, NULL, flags);
 
    /* Set the range of TIDs to scan */
    sscan->rs_rd->rd_tableam->scan_set_tidrange(sscan, mintid, maxtid);
 
    return sscan;
}
 
/*
 * table_rescan_tidrange resets the scan position and sets the minimum and
 * maximum TID range to scan for a TableScanDesc created by
 * table_beginscan_tidrange.
 */
static inline void
table_rescan_tidrange(TableScanDesc sscan, ItemPointer mintid,
                      ItemPointer maxtid)
{
    /* Ensure table_beginscan_tidrange() was used. */
    Assert((sscan->rs_flags & SO_TYPE_TIDRANGESCAN) != 0);
 
    sscan->rs_rd->rd_tableam->scan_rescan(sscan, NULL, false, false, false, false);
    sscan->rs_rd->rd_tableam->scan_set_tidrange(sscan, mintid, maxtid);
}
 
/*
 * Fetch the next tuple from `sscan` for a TID range scan created by
 * table_beginscan_tidrange().  Stores the tuple in `slot` and returns true,
 * or returns false if no more tuples exist in the range.
 */
static inline bool
table_scan_getnextslot_tidrange(TableScanDesc sscan, ScanDirection direction,
                                TupleTableSlot *slot)
{
    /* Ensure table_beginscan_tidrange() was used. */
    Assert((sscan->rs_flags & SO_TYPE_TIDRANGESCAN) != 0);
 
    /* We don't expect actual scans using NoMovementScanDirection */
    Assert(direction == ForwardScanDirection ||
           direction == BackwardScanDirection);
 
    return sscan->rs_rd->rd_tableam->scan_getnextslot_tidrange(sscan,
                                                               direction,
                                                               slot);
}
 
 
/* ----------------------------------------------------------------------------
 * Parallel table scan related functions.
 * ----------------------------------------------------------------------------
 */
 
/*
 * Estimate the size of shared memory needed for a parallel scan of this
 * relation.
 */
extern Size table_parallelscan_estimate(Relation rel, Snapshot snapshot);
 
/*
 * Initialize ParallelTableScanDesc for a parallel scan of this
 * relation. `pscan` needs to be sized according to parallelscan_estimate()
 * for the same relation.  Call this just once in the leader process; then,
 * individual workers attach via table_beginscan_parallel.
 */
extern void table_parallelscan_initialize(Relation rel,
                                          ParallelTableScanDesc pscan,
                                          Snapshot snapshot);
 
/*
 * Begin a parallel scan. `pscan` needs to have been initialized with
 * table_parallelscan_initialize(), for the same relation. The initialization
 * does not need to have happened in this backend.
 *
 * Caller must hold a suitable lock on the relation.
 */
extern TableScanDesc table_beginscan_parallel(Relation relation,
                                              ParallelTableScanDesc pscan);
 
/*
 * Restart a parallel scan.  Call this in the leader process.  Caller is
 * responsible for making sure that all workers have finished the scan
 * beforehand.
 */
static inline void
table_parallelscan_reinitialize(Relation rel, ParallelTableScanDesc pscan)
{
    rel->rd_tableam->parallelscan_reinitialize(rel, pscan);
}
 
 
/* ----------------------------------------------------------------------------
 *  Index scan related functions.
 * ----------------------------------------------------------------------------
 */
 
/*
 * Prepare to fetch tuples from the relation, as needed when fetching tuples
 * for an index scan.
 *
 * Tuples for an index scan can then be fetched via table_index_fetch_tuple().
 */
static inline IndexFetchTableData *
table_index_fetch_begin(Relation rel)
{
    return rel->rd_tableam->index_fetch_begin(rel);
}
 
/*
 * Reset index fetch. Typically this will release cross index fetch resources
 * held in IndexFetchTableData.
 */
static inline void
table_index_fetch_reset(struct IndexFetchTableData *scan)
{
    scan->rel->rd_tableam->index_fetch_reset(scan);
}
 
/*
 * Release resources and deallocate index fetch.
 */
static inline void
table_index_fetch_end(struct IndexFetchTableData *scan)
{
    scan->rel->rd_tableam->index_fetch_end(scan);
}
 
/*
 * Fetches, as part of an index scan, tuple at `tid` into `slot`, after doing
 * a visibility test according to `snapshot`. If a tuple was found and passed
 * the visibility test, returns true, false otherwise. Note that *tid may be
 * modified when we return true (see later remarks on multiple row versions
 * reachable via a single index entry).
 *
 * *call_again needs to be false on the first call to table_index_fetch_tuple() for
 * a tid. If there potentially is another tuple matching the tid, *call_again
 * will be set to true, signaling that table_index_fetch_tuple() should be called
 * again for the same tid.
 *
 * *all_dead, if all_dead is not NULL, will be set to true by
 * table_index_fetch_tuple() iff it is guaranteed that no backend needs to see
 * that tuple. Index AMs can use that to avoid returning that tid in future
 * searches.
 *
 * The difference between this function and table_tuple_fetch_row_version()
 * is that this function returns the currently visible version of a row if
 * the AM supports storing multiple row versions reachable via a single index
 * entry (like heap's HOT). Whereas table_tuple_fetch_row_version() only
 * evaluates the tuple exactly at `tid`. Outside of index entry ->table tuple
 * lookups, table_tuple_fetch_row_version() is what's usually needed.
 */
static inline bool
table_index_fetch_tuple(struct IndexFetchTableData *scan,
                        ItemPointer tid,
                        Snapshot snapshot,
                        TupleTableSlot *slot,
                        bool *call_again, bool *all_dead)
{
    /*
     * We don't expect direct calls to table_index_fetch_tuple with valid
     * CheckXidAlive for catalog or regular tables.  See detailed comments in
     * xact.c where these variables are declared.
     */
    if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
        elog(ERROR, "unexpected table_index_fetch_tuple call during logical decoding");
 
    return scan->rel->rd_tableam->index_fetch_tuple(scan, tid, snapshot,
                                                    slot, call_again,
                                                    all_dead);
}
 
/*
 * This is a convenience wrapper around table_index_fetch_tuple() which
 * returns whether there are table tuple items corresponding to an index
 * entry.  This likely is only useful to verify if there's a conflict in a
 * unique index.
 */
extern bool table_index_fetch_tuple_check(Relation rel,
                                          ItemPointer tid,
                                          Snapshot snapshot,
                                          bool *all_dead);
 
 
/* ------------------------------------------------------------------------
 * Functions for non-modifying operations on individual tuples
 * ------------------------------------------------------------------------
 */
 
 
/*
 * Fetch tuple at `tid` into `slot`, after doing a visibility test according to
 * `snapshot`. If a tuple was found and passed the visibility test, returns
 * true, false otherwise.
 *
 * See table_index_fetch_tuple's comment about what the difference between
 * these functions is. It is correct to use this function outside of index
 * entry->table tuple lookups.
 */
static inline bool
table_tuple_fetch_row_version(Relation rel,
                              ItemPointer tid,
                              Snapshot snapshot,
                              TupleTableSlot *slot)
{
    /*
     * We don't expect direct calls to table_tuple_fetch_row_version with
     * valid CheckXidAlive for catalog or regular tables.  See detailed
     * comments in xact.c where these variables are declared.
     */
    if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
        elog(ERROR, "unexpected table_tuple_fetch_row_version call during logical decoding");
 
    return rel->rd_tableam->tuple_fetch_row_version(rel, tid, snapshot, slot);
}
 
/*
 * Verify that `tid` is a potentially valid tuple identifier. That doesn't
 * mean that the pointed to row needs to exist or be visible, but that
 * attempting to fetch the row (e.g. with table_tuple_get_latest_tid() or
 * table_tuple_fetch_row_version()) should not error out if called with that
 * tid.
 *
 * `scan` needs to have been started via table_beginscan().
 */
static inline bool
table_tuple_tid_valid(TableScanDesc scan, ItemPointer tid)
{
    return scan->rs_rd->rd_tableam->tuple_tid_valid(scan, tid);
}
 
/*
 * Return the latest version of the tuple at `tid`, by updating `tid` to
 * point at the newest version.
 */
extern void table_tuple_get_latest_tid(TableScanDesc scan, ItemPointer tid);
 
/*
 * Return true iff tuple in slot satisfies the snapshot.
 *
 * This assumes the slot's tuple is valid, and of the appropriate type for the
 * AM.
 *
 * Some AMs might modify the data underlying the tuple as a side-effect. If so
 * they ought to mark the relevant buffer dirty.
 */
static inline bool
table_tuple_satisfies_snapshot(Relation rel, TupleTableSlot *slot,
                               Snapshot snapshot)
{
    return rel->rd_tableam->tuple_satisfies_snapshot(rel, slot, snapshot);
}
 
/*
 * Determine which index tuples are safe to delete based on their table TID.
 *
 * Determines which entries from index AM caller's TM_IndexDeleteOp state
 * point to vacuumable table tuples.  Entries that are found by tableam to be
 * vacuumable are naturally safe for index AM to delete, and so get directly
 * marked as deletable.  See comments above TM_IndexDelete and comments above
 * TM_IndexDeleteOp for full details.
 *
 * Returns a snapshotConflictHorizon transaction ID that caller places in
 * its index deletion WAL record.  This might be used during subsequent REDO
 * of the WAL record when in Hot Standby mode -- a recovery conflict for the
 * index deletion operation might be required on the standby.
 */
static inline TransactionId
table_index_delete_tuples(Relation rel, TM_IndexDeleteOp *delstate)
{
    return rel->rd_tableam->index_delete_tuples(rel, delstate);
}
 
 
/* ----------------------------------------------------------------------------
 *  Functions for manipulations of physical tuples.
 * ----------------------------------------------------------------------------
 */
 
/*
 * Insert a tuple from a slot into table AM routine.
 *
 * The options bitmask allows the caller to specify options that may change the
 * behaviour of the AM. The AM will ignore options that it does not support.
 *
 * If the TABLE_INSERT_SKIP_FSM option is specified, AMs are free to not reuse
 * free space in the relation. This can save some cycles when we know the
 * relation is new and doesn't contain useful amounts of free space.
 * TABLE_INSERT_SKIP_FSM is commonly passed directly to
 * RelationGetBufferForTuple. See that method for more information.
 *
 * TABLE_INSERT_FROZEN should only be specified for inserts into
 * relation storage created during the current subtransaction and when
 * there are no prior snapshots or pre-existing portals open.
 * This causes rows to be frozen, which is an MVCC violation and
 * requires explicit options chosen by user.
 *
 * TABLE_INSERT_NO_LOGICAL force-disables the emitting of logical decoding
 * information for the tuple. This should solely be used during table rewrites
 * where RelationIsLogicallyLogged(relation) is not yet accurate for the new
 * relation.
 *
 * Note that most of these options will be applied when inserting into the
 * heap's TOAST table, too, if the tuple requires any out-of-line data.
 *
 * The BulkInsertState object (if any; bistate can be NULL for default
 * behavior) is also just passed through to RelationGetBufferForTuple. If
 * `bistate` is provided, table_finish_bulk_insert() needs to be called.
 *
 * On return the slot's tts_tid and tts_tableOid are updated to reflect the
 * insertion. But note that any toasting of fields within the slot is NOT
 * reflected in the slots contents.
 */
static inline void
table_tuple_insert(Relation rel, TupleTableSlot *slot, CommandId cid,
                   int options, struct BulkInsertStateData *bistate)
{
    rel->rd_tableam->tuple_insert(rel, slot, cid, options,
                                  bistate);
}
 
/*
 * Perform a "speculative insertion". These can be backed out afterwards
 * without aborting the whole transaction.  Other sessions can wait for the
 * speculative insertion to be confirmed, turning it into a regular tuple, or
 * aborted, as if it never existed.  Speculatively inserted tuples behave as
 * "value locks" of short duration, used to implement INSERT .. ON CONFLICT.
 *
 * A transaction having performed a speculative insertion has to either abort,
 * or finish the speculative insertion with
 * table_tuple_complete_speculative(succeeded = ...).
 */
static inline void
table_tuple_insert_speculative(Relation rel, TupleTableSlot *slot,
                               CommandId cid, int options,
                               struct BulkInsertStateData *bistate,
                               uint32 specToken)
{
    rel->rd_tableam->tuple_insert_speculative(rel, slot, cid, options,
                                              bistate, specToken);
}
 
/*
 * Complete "speculative insertion" started in the same transaction. If
 * succeeded is true, the tuple is fully inserted, if false, it's removed.
 */
static inline void
table_tuple_complete_speculative(Relation rel, TupleTableSlot *slot,
                                 uint32 specToken, bool succeeded)
{
    rel->rd_tableam->tuple_complete_speculative(rel, slot, specToken,
                                                succeeded);
}
 
/*
 * Insert multiple tuples into a table.
 *
 * This is like table_tuple_insert(), but inserts multiple tuples in one
 * operation. That's often faster than calling table_tuple_insert() in a loop,
 * because e.g. the AM can reduce WAL logging and page locking overhead.
 *
 * Except for taking `nslots` tuples as input, and an array of TupleTableSlots
 * in `slots`, the parameters for table_multi_insert() are the same as for
 * table_tuple_insert().
 *
 * Note: this leaks memory into the current memory context. You can create a
 * temporary context before calling this, if that's a problem.
 */
static inline void
table_multi_insert(Relation rel, TupleTableSlot **slots, int nslots,
                   CommandId cid, int options, struct BulkInsertStateData *bistate)
{
    rel->rd_tableam->multi_insert(rel, slots, nslots,
                                  cid, options, bistate);
}
 
/*
 * Delete a tuple.
 *
 * NB: do not call this directly unless prepared to deal with
 * concurrent-update conditions.  Use simple_table_tuple_delete instead.
 *
 * Input parameters:
 *  relation - table to be modified (caller must hold suitable lock)
 *  tid - TID of tuple to be deleted
 *  cid - delete command ID (used for visibility test, and stored into
 *      cmax if successful)
 *  crosscheck - if not InvalidSnapshot, also check tuple against this
 *  wait - true if should wait for any conflicting update to commit/abort
 * Output parameters:
 *  tmfd - filled in failure cases (see below)
 *  changingPart - true iff the tuple is being moved to another partition
 *      table due to an update of the partition key. Otherwise, false.
 *
 * Normal, successful return value is TM_Ok, which means we did actually
 * delete it.  Failure return codes are TM_SelfModified, TM_Updated, and
 * TM_BeingModified (the last only possible if wait == false).
 *
 * In the failure cases, the routine fills *tmfd with the tuple's t_ctid,
 * t_xmax, and, if possible, t_cmax.  See comments for struct
 * TM_FailureData for additional info.
 */
static inline TM_Result
table_tuple_delete(Relation rel, ItemPointer tid, CommandId cid,
                   Snapshot snapshot, Snapshot crosscheck, bool wait,
                   TM_FailureData *tmfd, bool changingPart)
{
    return rel->rd_tableam->tuple_delete(rel, tid, cid,
                                         snapshot, crosscheck,
                                         wait, tmfd, changingPart);
}
 
/*
 * Update a tuple.
 *
 * NB: do not call this directly unless you are prepared to deal with
 * concurrent-update conditions.  Use simple_table_tuple_update instead.
 *
 * Input parameters:
 *  relation - table to be modified (caller must hold suitable lock)
 *  otid - TID of old tuple to be replaced
 *  slot - newly constructed tuple data to store
 *  cid - update command ID (used for visibility test, and stored into
 *      cmax/cmin if successful)
 *  crosscheck - if not InvalidSnapshot, also check old tuple against this
 *  wait - true if should wait for any conflicting update to commit/abort
 * Output parameters:
 *  tmfd - filled in failure cases (see below)
 *  lockmode - filled with lock mode acquired on tuple
 *  update_indexes - in success cases this is set to true if new index entries
 *      are required for this tuple
 *
 * Normal, successful return value is TM_Ok, which means we did actually
 * update it.  Failure return codes are TM_SelfModified, TM_Updated, and
 * TM_BeingModified (the last only possible if wait == false).
 *
 * On success, the slot's tts_tid and tts_tableOid are updated to match the new
 * stored tuple; in particular, slot->tts_tid is set to the TID where the
 * new tuple was inserted, and its HEAP_ONLY_TUPLE flag is set iff a HOT
 * update was done.  However, any TOAST changes in the new tuple's
 * data are not reflected into *newtup.
 *
 * In the failure cases, the routine fills *tmfd with the tuple's t_ctid,
 * t_xmax, and, if possible, t_cmax.  See comments for struct TM_FailureData
 * for additional info.
 */
static inline TM_Result
table_tuple_update(Relation rel, ItemPointer otid, TupleTableSlot *slot,
                   CommandId cid, Snapshot snapshot, Snapshot crosscheck,
                   bool wait, TM_FailureData *tmfd, LockTupleMode *lockmode,
                   TU_UpdateIndexes *update_indexes)
{
    return rel->rd_tableam->tuple_update(rel, otid, slot,
                                         cid, snapshot, crosscheck,
                                         wait, tmfd,
                                         lockmode, update_indexes);
}
 
/*
 * Lock a tuple in the specified mode.
 *
 * Input parameters:
 *  relation: relation containing tuple (caller must hold suitable lock)
 *  tid: TID of tuple to lock
 *  snapshot: snapshot to use for visibility determinations
 *  cid: current command ID (used for visibility test, and stored into
 *      tuple's cmax if lock is successful)
 *  mode: lock mode desired
 *  wait_policy: what to do if tuple lock is not available
 *  flags:
 *      If TUPLE_LOCK_FLAG_LOCK_UPDATE_IN_PROGRESS, follow the update chain to
 *      also lock descendant tuples if lock modes don't conflict.
 *      If TUPLE_LOCK_FLAG_FIND_LAST_VERSION, follow the update chain and lock
 *      latest version.
 *
 * Output parameters:
 *  *slot: contains the target tuple
 *  *tmfd: filled in failure cases (see below)
 *
 * Function result may be:
 *  TM_Ok: lock was successfully acquired
 *  TM_Invisible: lock failed because tuple was never visible to us
 *  TM_SelfModified: lock failed because tuple updated by self
 *  TM_Updated: lock failed because tuple updated by other xact
 *  TM_Deleted: lock failed because tuple deleted by other xact
 *  TM_WouldBlock: lock couldn't be acquired and wait_policy is skip
 *
 * In the failure cases other than TM_Invisible and TM_Deleted, the routine
 * fills *tmfd with the tuple's t_ctid, t_xmax, and, if possible, t_cmax.  See
 * comments for struct TM_FailureData for additional info.
 */
static inline TM_Result
table_tuple_lock(Relation rel, ItemPointer tid, Snapshot snapshot,
                 TupleTableSlot *slot, CommandId cid, LockTupleMode mode,
                 LockWaitPolicy wait_policy, uint8 flags,
                 TM_FailureData *tmfd)
{
    return rel->rd_tableam->tuple_lock(rel, tid, snapshot, slot,
                                       cid, mode, wait_policy,
                                       flags, tmfd);
}
 
/*
 * Perform operations necessary to complete insertions made via
 * tuple_insert and multi_insert with a BulkInsertState specified.
 */
static inline void
table_finish_bulk_insert(Relation rel, int options)
{
    /* optional callback */
    if (rel->rd_tableam && rel->rd_tableam->finish_bulk_insert)
        rel->rd_tableam->finish_bulk_insert(rel, options);
}
 
 
/* ------------------------------------------------------------------------
 * DDL related functionality.
 * ------------------------------------------------------------------------
 */
 
/*
 * Create storage for `rel` in `newrlocator`, with persistence set to
 * `persistence`.
 *
 * This is used both during relation creation and various DDL operations to
 * create new rel storage that can be filled from scratch.  When creating
 * new storage for an existing relfilelocator, this should be called before the
 * relcache entry has been updated.
 *
 * *freezeXid, *minmulti are set to the xid / multixact horizon for the table
 * that pg_class.{relfrozenxid, relminmxid} have to be set to.
 */
static inline void
table_relation_set_new_filelocator(Relation rel,
                                   const RelFileLocator *newrlocator,
                                   char persistence,
                                   TransactionId *freezeXid,
                                   MultiXactId *minmulti)
{
    rel->rd_tableam->relation_set_new_filelocator(rel, newrlocator,
                                                  persistence, freezeXid,
                                                  minmulti);
}
 
/*
 * Remove all table contents from `rel`, in a non-transactional manner.
 * Non-transactional meaning that there's no need to support rollbacks. This
 * commonly only is used to perform truncations for relation storage created in
 * the current transaction.
 */
static inline void
table_relation_nontransactional_truncate(Relation rel)
{
    rel->rd_tableam->relation_nontransactional_truncate(rel);
}
 
/*
 * Copy data from `rel` into the new relfilelocator `newrlocator`. The new
 * relfilelocator may not have storage associated before this function is
 * called. This is only supposed to be used for low level operations like
 * changing a relation's tablespace.
 */
static inline void
table_relation_copy_data(Relation rel, const RelFileLocator *newrlocator)
{
    rel->rd_tableam->relation_copy_data(rel, newrlocator);
}
 
/*
 * Copy data from `OldTable` into `NewTable`, as part of a CLUSTER or VACUUM
 * FULL.
 *
 * Additional Input parameters:
 * - use_sort - if true, the table contents are sorted appropriate for
 *   `OldIndex`; if false and OldIndex is not InvalidOid, the data is copied
 *   in that index's order; if false and OldIndex is InvalidOid, no sorting is
 *   performed
 * - OldIndex - see use_sort
 * - OldestXmin - computed by vacuum_get_cutoffs(), even when
 *   not needed for the relation's AM
 * - *xid_cutoff - ditto
 * - *multi_cutoff - ditto
 *
 * Output parameters:
 * - *xid_cutoff - rel's new relfrozenxid value, may be invalid
 * - *multi_cutoff - rel's new relminmxid value, may be invalid
 * - *tups_vacuumed - stats, for logging, if appropriate for AM
 * - *tups_recently_dead - stats, for logging, if appropriate for AM
 */
static inline void
table_relation_copy_for_cluster(Relation OldTable, Relation NewTable,
                                Relation OldIndex,
                                bool use_sort,
                                TransactionId OldestXmin,
                                TransactionId *xid_cutoff,
                                MultiXactId *multi_cutoff,
                                double *num_tuples,
                                double *tups_vacuumed,
                                double *tups_recently_dead)
{
    OldTable->rd_tableam->relation_copy_for_cluster(OldTable, NewTable, OldIndex,
                                                    use_sort, OldestXmin,
                                                    xid_cutoff, multi_cutoff,
                                                    num_tuples, tups_vacuumed,
                                                    tups_recently_dead);
}
 
/*
 * Perform VACUUM on the relation. The VACUUM can be triggered by a user or by
 * autovacuum. The specific actions performed by the AM will depend heavily on
 * the individual AM.
 *
 * On entry a transaction needs to already been established, and the
 * table is locked with a ShareUpdateExclusive lock.
 *
 * Note that neither VACUUM FULL (and CLUSTER), nor ANALYZE go through this
 * routine, even if (for ANALYZE) it is part of the same VACUUM command.
 */
static inline void
table_relation_vacuum(Relation rel, struct VacuumParams *params,
                      BufferAccessStrategy bstrategy)
{
    rel->rd_tableam->relation_vacuum(rel, params, bstrategy);
}
 
/*
 * Prepare to analyze the next block in the read stream. The scan needs to
 * have been  started with table_beginscan_analyze().  Note that this routine
 * might acquire resources like locks that are held until
 * table_scan_analyze_next_tuple() returns false.
 *
 * Returns false if block is unsuitable for sampling, true otherwise.
 */
static inline bool
table_scan_analyze_next_block(TableScanDesc scan, ReadStream *stream)
{
    return scan->rs_rd->rd_tableam->scan_analyze_next_block(scan, stream);
}
 
/*
 * Iterate over tuples in the block selected with
 * table_scan_analyze_next_block() (which needs to have returned true, and
 * this routine may not have returned false for the same block before). If a
 * tuple that's suitable for sampling is found, true is returned and a tuple
 * is stored in `slot`.
 *
 * *liverows and *deadrows are incremented according to the encountered
 * tuples.
 */
static inline bool
table_scan_analyze_next_tuple(TableScanDesc scan, TransactionId OldestXmin,
                              double *liverows, double *deadrows,
                              TupleTableSlot *slot)
{
    return scan->rs_rd->rd_tableam->scan_analyze_next_tuple(scan, OldestXmin,
                                                            liverows, deadrows,
                                                            slot);
}
 
/*
 * table_index_build_scan - scan the table to find tuples to be indexed
 *
 * This is called back from an access-method-specific index build procedure
 * after the AM has done whatever setup it needs.  The parent table relation
 * is scanned to find tuples that should be entered into the index.  Each
 * such tuple is passed to the AM's callback routine, which does the right
 * things to add it to the new index.  After we return, the AM's index
 * build procedure does whatever cleanup it needs.
 *
 * The total count of live tuples is returned.  This is for updating pg_class
 * statistics.  (It's annoying not to be able to do that here, but we want to
 * merge that update with others; see index_update_stats.)  Note that the
 * index AM itself must keep track of the number of index tuples; we don't do
 * so here because the AM might reject some of the tuples for its own reasons,
 * such as being unable to store NULLs.
 *
 * If 'progress', the PROGRESS_SCAN_BLOCKS_TOTAL counter is updated when
 * starting the scan, and PROGRESS_SCAN_BLOCKS_DONE is updated as we go along.
 *
 * A side effect is to set indexInfo->ii_BrokenHotChain to true if we detect
 * any potentially broken HOT chains.  Currently, we set this if there are any
 * RECENTLY_DEAD or DELETE_IN_PROGRESS entries in a HOT chain, without trying
 * very hard to detect whether they're really incompatible with the chain tip.
 * This only really makes sense for heap AM, it might need to be generalized
 * for other AMs later.
 */
static inline double
table_index_build_scan(Relation table_rel,
                       Relation index_rel,
                       struct IndexInfo *index_info,
                       bool allow_sync,
                       bool progress,
                       IndexBuildCallback callback,
                       void *callback_state,
                       TableScanDesc scan)
{
    return table_rel->rd_tableam->index_build_range_scan(table_rel,
                                                         index_rel,
                                                         index_info,
                                                         allow_sync,
                                                         false,
                                                         progress,
                                                         0,
                                                         InvalidBlockNumber,
                                                         callback,
                                                         callback_state,
                                                         scan);
}
 
/*
 * As table_index_build_scan(), except that instead of scanning the complete
 * table, only the given number of blocks are scanned.  Scan to end-of-rel can
 * be signaled by passing InvalidBlockNumber as numblocks.  Note that
 * restricting the range to scan cannot be done when requesting syncscan.
 *
 * When "anyvisible" mode is requested, all tuples visible to any transaction
 * are indexed and counted as live, including those inserted or deleted by
 * transactions that are still in progress.
 */
static inline double
table_index_build_range_scan(Relation table_rel,
                             Relation index_rel,
                             struct IndexInfo *index_info,
                             bool allow_sync,
                             bool anyvisible,
                             bool progress,
                             BlockNumber start_blockno,
                             BlockNumber numblocks,
                             IndexBuildCallback callback,
                             void *callback_state,
                             TableScanDesc scan)
{
    return table_rel->rd_tableam->index_build_range_scan(table_rel,
                                                         index_rel,
                                                         index_info,
                                                         allow_sync,
                                                         anyvisible,
                                                         progress,
                                                         start_blockno,
                                                         numblocks,
                                                         callback,
                                                         callback_state,
                                                         scan);
}
 
/*
 * table_index_validate_scan - second table scan for concurrent index build
 *
 * See validate_index() for an explanation.
 */
static inline void
table_index_validate_scan(Relation table_rel,
                          Relation index_rel,
                          struct IndexInfo *index_info,
                          Snapshot snapshot,
                          struct ValidateIndexState *state)
{
    table_rel->rd_tableam->index_validate_scan(table_rel,
                                               index_rel,
                                               index_info,
                                               snapshot,
                                               state);
}
 
 
/* ----------------------------------------------------------------------------
 * Miscellaneous functionality
 * ----------------------------------------------------------------------------
 */
 
/*
 * Return the current size of `rel` in bytes. If `forkNumber` is
 * InvalidForkNumber, return the relation's overall size, otherwise the size
 * for the indicated fork.
 *
 * Note that the overall size might not be the equivalent of the sum of sizes
 * for the individual forks for some AMs, e.g. because the AMs storage does
 * not neatly map onto the builtin types of forks.
 */
static inline uint64
table_relation_size(Relation rel, ForkNumber forkNumber)
{
    return rel->rd_tableam->relation_size(rel, forkNumber);
}
 
/*
 * table_relation_needs_toast_table - does this relation need a toast table?
 */
static inline bool
table_relation_needs_toast_table(Relation rel)
{
    return rel->rd_tableam->relation_needs_toast_table(rel);
}
 
/*
 * Return the OID of the AM that should be used to implement the TOAST table
 * for this relation.
 */
static inline Oid
table_relation_toast_am(Relation rel)
{
    return rel->rd_tableam->relation_toast_am(rel);
}
 
/*
 * Fetch all or part of a TOAST value from a TOAST table.
 *
 * If this AM is never used to implement a TOAST table, then this callback
 * is not needed. But, if toasted values are ever stored in a table of this
 * type, then you will need this callback.
 *
 * toastrel is the relation in which the toasted value is stored.
 *
 * valueid identifies which toast value is to be fetched. For the heap,
 * this corresponds to the values stored in the chunk_id column.
 *
 * attrsize is the total size of the toast value to be fetched.
 *
 * sliceoffset is the offset within the toast value of the first byte that
 * should be fetched.
 *
 * slicelength is the number of bytes from the toast value that should be
 * fetched.
 *
 * result is caller-allocated space into which the fetched bytes should be
 * stored.
 */
static inline void
table_relation_fetch_toast_slice(Relation toastrel, Oid valueid,
                                 int32 attrsize, int32 sliceoffset,
                                 int32 slicelength, struct varlena *result)
{
    toastrel->rd_tableam->relation_fetch_toast_slice(toastrel, valueid,
                                                     attrsize,
                                                     sliceoffset, slicelength,
                                                     result);
}
 
 
/* ----------------------------------------------------------------------------
 * Planner related functionality
 * ----------------------------------------------------------------------------
 */
 
/*
 * Estimate the current size of the relation, as an AM specific workhorse for
 * estimate_rel_size(). Look there for an explanation of the parameters.
 */
static inline void
table_relation_estimate_size(Relation rel, int32 *attr_widths,
                             BlockNumber *pages, double *tuples,
                             double *allvisfrac)
{
    rel->rd_tableam->relation_estimate_size(rel, attr_widths, pages, tuples,
                                            allvisfrac);
}
 
 
/* ----------------------------------------------------------------------------
 * Executor related functionality
 * ----------------------------------------------------------------------------
 */
 
/*
 * Prepare to fetch / check / return tuples as part of a bitmap table scan.
 * `scan` needs to have been started via table_beginscan_bm(). Returns false
 * if there are no more blocks in the bitmap, true otherwise.
 *
 * `lossy_pages` and `exact_pages` are EXPLAIN counters that can be
 * incremented by the table AM to indicate whether or not the block's
 * representation in the bitmap is lossy.
 *
 * `recheck` is set by the table AM to indicate whether or not the tuples
 * from this block should be rechecked.
 *
 * `blockno` is the current block and is set by the table AM and is used by
 * bitmap table scan code to validate that the prefetch block stays ahead of
 * the current block.
 *
 * Note, this is an optionally implemented function, therefore should only be
 * used after verifying the presence (at plan time or such).
 */
static inline bool
table_scan_bitmap_next_block(TableScanDesc scan,
                             BlockNumber *blockno,
                             bool *recheck,
                             uint64 *lossy_pages,
                             uint64 *exact_pages)
{
    /*
     * We don't expect direct calls to table_scan_bitmap_next_block with valid
     * CheckXidAlive for catalog or regular tables.  See detailed comments in
     * xact.c where these variables are declared.
     */
    if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
        elog(ERROR, "unexpected table_scan_bitmap_next_block call during logical decoding");
 
    return scan->rs_rd->rd_tableam->scan_bitmap_next_block(scan,
                                                           blockno, recheck,
                                                           lossy_pages,
                                                           exact_pages);
}
 
/*
 * Fetch the next tuple of a bitmap table scan into `slot` and return true if
 * a visible tuple was found, false otherwise.
 * table_scan_bitmap_next_block() needs to previously have selected a
 * block (i.e. returned true), and no previous
 * table_scan_bitmap_next_tuple() for the same block may have
 * returned false.
 */
static inline bool
table_scan_bitmap_next_tuple(TableScanDesc scan,
                             TupleTableSlot *slot)
{
    /*
     * We don't expect direct calls to table_scan_bitmap_next_tuple with valid
     * CheckXidAlive for catalog or regular tables.  See detailed comments in
     * xact.c where these variables are declared.
     */
    if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
        elog(ERROR, "unexpected table_scan_bitmap_next_tuple call during logical decoding");
 
    return scan->rs_rd->rd_tableam->scan_bitmap_next_tuple(scan,
                                                           slot);
}
 
/*
 * Prepare to fetch tuples from the next block in a sample scan. Returns false
 * if the sample scan is finished, true otherwise. `scan` needs to have been
 * started via table_beginscan_sampling().
 *
 * This will call the TsmRoutine's NextSampleBlock() callback if necessary
 * (i.e. NextSampleBlock is not NULL), or perform a sequential scan over the
 * underlying relation.
 */
static inline bool
table_scan_sample_next_block(TableScanDesc scan,
                             struct SampleScanState *scanstate)
{
    /*
     * We don't expect direct calls to table_scan_sample_next_block with valid
     * CheckXidAlive for catalog or regular tables.  See detailed comments in
     * xact.c where these variables are declared.
     */
    if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
        elog(ERROR, "unexpected table_scan_sample_next_block call during logical decoding");
    return scan->rs_rd->rd_tableam->scan_sample_next_block(scan, scanstate);
}
 
/*
 * Fetch the next sample tuple into `slot` and return true if a visible tuple
 * was found, false otherwise. table_scan_sample_next_block() needs to
 * previously have selected a block (i.e. returned true), and no previous
 * table_scan_sample_next_tuple() for the same block may have returned false.
 *
 * This will call the TsmRoutine's NextSampleTuple() callback.
 */
static inline bool
table_scan_sample_next_tuple(TableScanDesc scan,
                             struct SampleScanState *scanstate,
                             TupleTableSlot *slot)
{
    /*
     * We don't expect direct calls to table_scan_sample_next_tuple with valid
     * CheckXidAlive for catalog or regular tables.  See detailed comments in
     * xact.c where these variables are declared.
     */
    if (unlikely(TransactionIdIsValid(CheckXidAlive) && !bsysscan))
        elog(ERROR, "unexpected table_scan_sample_next_tuple call during logical decoding");
    return scan->rs_rd->rd_tableam->scan_sample_next_tuple(scan, scanstate,
                                                           slot);
}
 
 
/* ----------------------------------------------------------------------------
 * Functions to make modifications a bit simpler.
 * ----------------------------------------------------------------------------
 */
 
extern void simple_table_tuple_insert(Relation rel, TupleTableSlot *slot);
extern void simple_table_tuple_delete(Relation rel, ItemPointer tid,
                                      Snapshot snapshot);
extern void simple_table_tuple_update(Relation rel, ItemPointer otid,
                                      TupleTableSlot *slot, Snapshot snapshot,
                                      TU_UpdateIndexes *update_indexes);
 
 
/* ----------------------------------------------------------------------------
 * Helper functions to implement parallel scans for block oriented AMs.
 * ----------------------------------------------------------------------------
 */
 
extern Size table_block_parallelscan_estimate(Relation rel);
extern Size table_block_parallelscan_initialize(Relation rel,
                                                ParallelTableScanDesc pscan);
extern void table_block_parallelscan_reinitialize(Relation rel,
                                                  ParallelTableScanDesc pscan);
extern BlockNumber table_block_parallelscan_nextpage(Relation rel,
                                                     ParallelBlockTableScanWorker pbscanwork,
                                                     ParallelBlockTableScanDesc pbscan);
extern void table_block_parallelscan_startblock_init(Relation rel,
                                                     ParallelBlockTableScanWorker pbscanwork,
                                                     ParallelBlockTableScanDesc pbscan);
 
 
/* ----------------------------------------------------------------------------
 * Helper functions to implement relation sizing for block oriented AMs.
 * ----------------------------------------------------------------------------
 */
 
extern uint64 table_block_relation_size(Relation rel, ForkNumber forkNumber);
extern void table_block_relation_estimate_size(Relation rel,
                                               int32 *attr_widths,
                                               BlockNumber *pages,
                                               double *tuples,
                                               double *allvisfrac,
                                               Size overhead_bytes_per_tuple,
                                               Size usable_bytes_per_page);
 
/* ----------------------------------------------------------------------------
 * Functions in tableamapi.c
 * ----------------------------------------------------------------------------
 */
 
extern const TableAmRoutine *GetTableAmRoutine(Oid amhandler);
 
/* ----------------------------------------------------------------------------
 * Functions in heapam_handler.c
 * ----------------------------------------------------------------------------
 */
 
extern const TableAmRoutine *GetHeapamTableAmRoutine(void);
 
#endif                          /* TABLEAM_H */