relscan.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * relscan.h
 *    POSTGRES relation scan descriptor definitions.
 *
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/relscan.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef RELSCAN_H
#define RELSCAN_H

#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/itup.h"
#include "access/tupdesc.h"
#include "storage/spin.h"

/*
 * Shared state for parallel heap scan.
 *
 * Each backend participating in a parallel heap scan has its own
 * HeapScanDesc in backend-private memory, and those objects all contain
 * a pointer to this structure.  The information here must be sufficient
 * to properly initialize each new HeapScanDesc as workers join the scan,
 * and it must act as a font of block numbers for those workers.
 */
typedef struct ParallelHeapScanDescData
{
    Oid         phs_relid;      /* OID of relation to scan */
    bool        phs_syncscan;   /* report location to syncscan logic? */
    BlockNumber phs_nblocks;    /* # blocks in relation at start of scan */
    slock_t     phs_mutex;      /* mutual exclusion for block number fields */
    BlockNumber phs_startblock; /* starting block number */
    BlockNumber phs_cblock;     /* current block number */
    char        phs_snapshot_data[FLEXIBLE_ARRAY_MEMBER];
}   ParallelHeapScanDescData;

typedef struct HeapScanDescData
{
    /* scan parameters */
    Relation    rs_rd;          /* heap relation descriptor */
    Snapshot    rs_snapshot;    /* snapshot to see */
    int         rs_nkeys;       /* number of scan keys */
    ScanKey     rs_key;         /* array of scan key descriptors */
    bool        rs_bitmapscan;  /* true if this is really a bitmap scan */
    bool        rs_samplescan;  /* true if this is really a sample scan */
    bool        rs_pageatatime; /* verify visibility page-at-a-time? */
    bool        rs_allow_strat; /* allow or disallow use of access strategy */
    bool        rs_allow_sync;  /* allow or disallow use of syncscan */
    bool        rs_temp_snap;   /* unregister snapshot at scan end? */

    /* state set up at initscan time */
    BlockNumber rs_nblocks;     /* total number of blocks in rel */
    BlockNumber rs_startblock;  /* block # to start at */
    BlockNumber rs_numblocks;   /* max number of blocks to scan */
    /* rs_numblocks is usually InvalidBlockNumber, meaning "scan whole rel" */
    BufferAccessStrategy rs_strategy;   /* access strategy for reads */
    bool        rs_syncscan;    /* report location to syncscan logic? */

    /* scan current state */
    bool        rs_inited;      /* false = scan not init'd yet */
    HeapTupleData rs_ctup;      /* current tuple in scan, if any */
    BlockNumber rs_cblock;      /* current block # in scan, if any */
    Buffer      rs_cbuf;        /* current buffer in scan, if any */
    /* NB: if rs_cbuf is not InvalidBuffer, we hold a pin on that buffer */
    ParallelHeapScanDesc rs_parallel;   /* parallel scan information */

    /* these fields only used in page-at-a-time mode and for bitmap scans */
    int         rs_cindex;      /* current tuple's index in vistuples */
    int         rs_ntuples;     /* number of visible tuples on page */
    OffsetNumber rs_vistuples[MaxHeapTuplesPerPage];    /* their offsets */
}   HeapScanDescData;

/*
 * We use the same IndexScanDescData structure for both amgettuple-based
 * and amgetbitmap-based index scans.  Some fields are only relevant in
 * amgettuple-based scans.
 */
typedef struct IndexScanDescData
{
    /* scan parameters */
    Relation    heapRelation;   /* heap relation descriptor, or NULL */
    Relation    indexRelation;  /* index relation descriptor */
    Snapshot    xs_snapshot;    /* snapshot to see */
    int         numberOfKeys;   /* number of index qualifier conditions */
    int         numberOfOrderBys;       /* number of ordering operators */
    ScanKey     keyData;        /* array of index qualifier descriptors */
    ScanKey     orderByData;    /* array of ordering op descriptors */
    bool        xs_want_itup;   /* caller requests index tuples */
    bool        xs_temp_snap;   /* unregister snapshot at scan end? */

    /* signaling to index AM about killing index tuples */
    bool        kill_prior_tuple;       /* last-returned tuple is dead */
    bool        ignore_killed_tuples;   /* do not return killed entries */
    bool        xactStartedInRecovery;  /* prevents killing/seeing killed
                                         * tuples */

    /* index access method's private state */
    void       *opaque;         /* access-method-specific info */

    /*
     * In an index-only scan, a successful amgettuple call must fill either
     * xs_itup (and xs_itupdesc) or xs_hitup (and xs_hitupdesc) to provide the
     * data returned by the scan.  It can fill both, in which case the heap
     * format will be used.
     */
    IndexTuple  xs_itup;        /* index tuple returned by AM */
    TupleDesc   xs_itupdesc;    /* rowtype descriptor of xs_itup */
    HeapTuple   xs_hitup;       /* index data returned by AM, as HeapTuple */
    TupleDesc   xs_hitupdesc;   /* rowtype descriptor of xs_hitup */

    /* xs_ctup/xs_cbuf/xs_recheck are valid after a successful index_getnext */
    HeapTupleData xs_ctup;      /* current heap tuple, if any */
    Buffer      xs_cbuf;        /* current heap buffer in scan, if any */
    /* NB: if xs_cbuf is not InvalidBuffer, we hold a pin on that buffer */
    bool        xs_recheck;     /* T means scan keys must be rechecked */

    /*
     * When fetching with an ordering operator, the values of the ORDER BY
     * expressions of the last returned tuple, according to the index.  If
     * xs_recheckorderby is true, these need to be rechecked just like the
     * scan keys, and the values returned here are a lower-bound on the actual
     * values.
     */
    Datum      *xs_orderbyvals;
    bool       *xs_orderbynulls;
    bool        xs_recheckorderby;

    /* state data for traversing HOT chains in index_getnext */
    bool        xs_continue_hot;    /* T if must keep walking HOT chain */

    /* parallel index scan information, in shared memory */
    ParallelIndexScanDesc parallel_scan;
}   IndexScanDescData;

/* Generic structure for parallel scans */
typedef struct ParallelIndexScanDescData
{
    Oid         ps_relid;
    Oid         ps_indexid;
    Size        ps_offset;      /* Offset in bytes of am specific structure */
    char        ps_snapshot_data[FLEXIBLE_ARRAY_MEMBER];
}   ParallelIndexScanDescData;

/* Struct for heap-or-index scans of system tables */
typedef struct SysScanDescData
{
    Relation    heap_rel;       /* catalog being scanned */
    Relation    irel;           /* NULL if doing heap scan */
    HeapScanDesc scan;          /* only valid in heap-scan case */
    IndexScanDesc iscan;        /* only valid in index-scan case */
    Snapshot    snapshot;       /* snapshot to unregister at end of scan */
}   SysScanDescData;

#endif   /* RELSCAN_H */