relation.c

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/*-------------------------------------------------------------------------
 * relation.c
 *     PostgreSQL logical replication relation mapping cache
 *
 * Copyright (c) 2016-2023, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/replication/logical/relation.c
 *
 * NOTES
 *    Routines in this file mainly have to do with mapping the properties
 *    of local replication target relations to the properties of their
 *    remote counterpart.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#ifdef USE_ASSERT_CHECKING
#include "access/amapi.h"
#endif
#include "access/genam.h"
#include "access/table.h"
#include "catalog/namespace.h"
#include "catalog/pg_am_d.h"
#include "catalog/pg_subscription_rel.h"
#include "executor/executor.h"
#include "nodes/makefuncs.h"
#include "replication/logicalrelation.h"
#include "replication/worker_internal.h"
#include "utils/inval.h"
 
 
static MemoryContext LogicalRepRelMapContext = NULL;
 
static HTAB *LogicalRepRelMap = NULL;
 
/*
 * Partition map (LogicalRepPartMap)
 *
 * When a partitioned table is used as replication target, replicated
 * operations are actually performed on its leaf partitions, which requires
 * the partitions to also be mapped to the remote relation.  Parent's entry
 * (LogicalRepRelMapEntry) cannot be used as-is for all partitions, because
 * individual partitions may have different attribute numbers, which means
 * attribute mappings to remote relation's attributes must be maintained
 * separately for each partition.
 */
static MemoryContext LogicalRepPartMapContext = NULL;
static HTAB *LogicalRepPartMap = NULL;
typedef struct LogicalRepPartMapEntry
{
    Oid         partoid;        /* LogicalRepPartMap's key */
    LogicalRepRelMapEntry relmapentry;
} LogicalRepPartMapEntry;
 
static Oid  FindLogicalRepLocalIndex(Relation localrel, LogicalRepRelation *remoterel,
                                     AttrMap *attrMap);
 
/*
 * Relcache invalidation callback for our relation map cache.
 */
static void
logicalrep_relmap_invalidate_cb(Datum arg, Oid reloid)
{
    LogicalRepRelMapEntry *entry;
 
    /* Just to be sure. */
    if (LogicalRepRelMap == NULL)
        return;
 
    if (reloid != InvalidOid)
    {
        HASH_SEQ_STATUS status;
 
        hash_seq_init(&status, LogicalRepRelMap);
 
        /* TODO, use inverse lookup hashtable? */
        while ((entry = (LogicalRepRelMapEntry *) hash_seq_search(&status)) != NULL)
        {
            if (entry->localreloid == reloid)
            {
                entry->localrelvalid = false;
                hash_seq_term(&status);
                break;
            }
        }
    }
    else
    {
        /* invalidate all cache entries */
        HASH_SEQ_STATUS status;
 
        hash_seq_init(&status, LogicalRepRelMap);
 
        while ((entry = (LogicalRepRelMapEntry *) hash_seq_search(&status)) != NULL)
            entry->localrelvalid = false;
    }
}
 
/*
 * Initialize the relation map cache.
 */
static void
logicalrep_relmap_init(void)
{
    HASHCTL     ctl;
 
    if (!LogicalRepRelMapContext)
        LogicalRepRelMapContext =
            AllocSetContextCreate(CacheMemoryContext,
                                  "LogicalRepRelMapContext",
                                  ALLOCSET_DEFAULT_SIZES);
 
    /* Initialize the relation hash table. */
    ctl.keysize = sizeof(LogicalRepRelId);
    ctl.entrysize = sizeof(LogicalRepRelMapEntry);
    ctl.hcxt = LogicalRepRelMapContext;
 
    LogicalRepRelMap = hash_create("logicalrep relation map cache", 128, &ctl,
                                   HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 
    /* Watch for invalidation events. */
    CacheRegisterRelcacheCallback(logicalrep_relmap_invalidate_cb,
                                  (Datum) 0);
}
 
/*
 * Free the entry of a relation map cache.
 */
static void
logicalrep_relmap_free_entry(LogicalRepRelMapEntry *entry)
{
    LogicalRepRelation *remoterel;
 
    remoterel = &entry->remoterel;
 
    pfree(remoterel->nspname);
    pfree(remoterel->relname);
 
    if (remoterel->natts > 0)
    {
        int         i;
 
        for (i = 0; i < remoterel->natts; i++)
            pfree(remoterel->attnames[i]);
 
        pfree(remoterel->attnames);
        pfree(remoterel->atttyps);
    }
    bms_free(remoterel->attkeys);
 
    if (entry->attrmap)
        free_attrmap(entry->attrmap);
}
 
/*
 * Add new entry or update existing entry in the relation map cache.
 *
 * Called when new relation mapping is sent by the publisher to update
 * our expected view of incoming data from said publisher.
 */
void
logicalrep_relmap_update(LogicalRepRelation *remoterel)
{
    MemoryContext oldctx;
    LogicalRepRelMapEntry *entry;
    bool        found;
    int         i;
 
    if (LogicalRepRelMap == NULL)
        logicalrep_relmap_init();
 
    /*
     * HASH_ENTER returns the existing entry if present or creates a new one.
     */
    entry = hash_search(LogicalRepRelMap, &remoterel->remoteid,
                        HASH_ENTER, &found);
 
    if (found)
        logicalrep_relmap_free_entry(entry);
 
    memset(entry, 0, sizeof(LogicalRepRelMapEntry));
 
    /* Make cached copy of the data */
    oldctx = MemoryContextSwitchTo(LogicalRepRelMapContext);
    entry->remoterel.remoteid = remoterel->remoteid;
    entry->remoterel.nspname = pstrdup(remoterel->nspname);
    entry->remoterel.relname = pstrdup(remoterel->relname);
    entry->remoterel.natts = remoterel->natts;
    entry->remoterel.attnames = palloc(remoterel->natts * sizeof(char *));
    entry->remoterel.atttyps = palloc(remoterel->natts * sizeof(Oid));
    for (i = 0; i < remoterel->natts; i++)
    {
        entry->remoterel.attnames[i] = pstrdup(remoterel->attnames[i]);
        entry->remoterel.atttyps[i] = remoterel->atttyps[i];
    }
    entry->remoterel.replident = remoterel->replident;
    entry->remoterel.attkeys = bms_copy(remoterel->attkeys);
    MemoryContextSwitchTo(oldctx);
}
 
/*
 * Find attribute index in TupleDesc struct by attribute name.
 *
 * Returns -1 if not found.
 */
static int
logicalrep_rel_att_by_name(LogicalRepRelation *remoterel, const char *attname)
{
    int         i;
 
    for (i = 0; i < remoterel->natts; i++)
    {
        if (strcmp(remoterel->attnames[i], attname) == 0)
            return i;
    }
 
    return -1;
}
 
/*
 * Report error with names of the missing local relation column(s), if any.
 */
static void
logicalrep_report_missing_attrs(LogicalRepRelation *remoterel,
                                Bitmapset *missingatts)
{
    if (!bms_is_empty(missingatts))
    {
        StringInfoData missingattsbuf;
        int         missingattcnt = 0;
        int         i;
 
        initStringInfo(&missingattsbuf);
 
        i = -1;
        while ((i = bms_next_member(missingatts, i)) >= 0)
        {
            missingattcnt++;
            if (missingattcnt == 1)
                appendStringInfo(&missingattsbuf, _("\"%s\""),
                                 remoterel->attnames[i]);
            else
                appendStringInfo(&missingattsbuf, _(", \"%s\""),
                                 remoterel->attnames[i]);
        }
 
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg_plural("logical replication target relation \"%s.%s\" is missing replicated column: %s",
                               "logical replication target relation \"%s.%s\" is missing replicated columns: %s",
                               missingattcnt,
                               remoterel->nspname,
                               remoterel->relname,
                               missingattsbuf.data)));
    }
}
 
/*
 * Check if replica identity matches and mark the updatable flag.
 *
 * We allow for stricter replica identity (fewer columns) on subscriber as
 * that will not stop us from finding unique tuple. IE, if publisher has
 * identity (id,timestamp) and subscriber just (id) this will not be a
 * problem, but in the opposite scenario it will.
 *
 * We just mark the relation entry as not updatable here if the local
 * replica identity is found to be insufficient for applying
 * updates/deletes (inserts don't care!) and leave it to
 * check_relation_updatable() to throw the actual error if needed.
 */
static void
logicalrep_rel_mark_updatable(LogicalRepRelMapEntry *entry)
{
    Bitmapset  *idkey;
    LogicalRepRelation *remoterel = &entry->remoterel;
    int         i;
 
    entry->updatable = true;
 
    idkey = RelationGetIndexAttrBitmap(entry->localrel,
                                       INDEX_ATTR_BITMAP_IDENTITY_KEY);
    /* fallback to PK if no replica identity */
    if (idkey == NULL)
    {
        idkey = RelationGetIndexAttrBitmap(entry->localrel,
                                           INDEX_ATTR_BITMAP_PRIMARY_KEY);
 
        /*
         * If no replica identity index and no PK, the published table must
         * have replica identity FULL.
         */
        if (idkey == NULL && remoterel->replident != REPLICA_IDENTITY_FULL)
            entry->updatable = false;
    }
 
    i = -1;
    while ((i = bms_next_member(idkey, i)) >= 0)
    {
        int         attnum = i + FirstLowInvalidHeapAttributeNumber;
 
        if (!AttrNumberIsForUserDefinedAttr(attnum))
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("logical replication target relation \"%s.%s\" uses "
                            "system columns in REPLICA IDENTITY index",
                            remoterel->nspname, remoterel->relname)));
 
        attnum = AttrNumberGetAttrOffset(attnum);
 
        if (entry->attrmap->attnums[attnum] < 0 ||
            !bms_is_member(entry->attrmap->attnums[attnum], remoterel->attkeys))
        {
            entry->updatable = false;
            break;
        }
    }
}
 
/*
 * Open the local relation associated with the remote one.
 *
 * Rebuilds the Relcache mapping if it was invalidated by local DDL.
 */
LogicalRepRelMapEntry *
logicalrep_rel_open(LogicalRepRelId remoteid, LOCKMODE lockmode)
{
    LogicalRepRelMapEntry *entry;
    bool        found;
    LogicalRepRelation *remoterel;
 
    if (LogicalRepRelMap == NULL)
        logicalrep_relmap_init();
 
    /* Search for existing entry. */
    entry = hash_search(LogicalRepRelMap, &remoteid,
                        HASH_FIND, &found);
 
    if (!found)
        elog(ERROR, "no relation map entry for remote relation ID %u",
             remoteid);
 
    remoterel = &entry->remoterel;
 
    /* Ensure we don't leak a relcache refcount. */
    if (entry->localrel)
        elog(ERROR, "remote relation ID %u is already open", remoteid);
 
    /*
     * When opening and locking a relation, pending invalidation messages are
     * processed which can invalidate the relation.  Hence, if the entry is
     * currently considered valid, try to open the local relation by OID and
     * see if invalidation ensues.
     */
    if (entry->localrelvalid)
    {
        entry->localrel = try_table_open(entry->localreloid, lockmode);
        if (!entry->localrel)
        {
            /* Table was renamed or dropped. */
            entry->localrelvalid = false;
        }
        else if (!entry->localrelvalid)
        {
            /* Note we release the no-longer-useful lock here. */
            table_close(entry->localrel, lockmode);
            entry->localrel = NULL;
        }
    }
 
    /*
     * If the entry has been marked invalid since we last had lock on it,
     * re-open the local relation by name and rebuild all derived data.
     */
    if (!entry->localrelvalid)
    {
        Oid         relid;
        TupleDesc   desc;
        MemoryContext oldctx;
        int         i;
        Bitmapset  *missingatts;
 
        /* Release the no-longer-useful attrmap, if any. */
        if (entry->attrmap)
        {
            free_attrmap(entry->attrmap);
            entry->attrmap = NULL;
        }
 
        /* Try to find and lock the relation by name. */
        relid = RangeVarGetRelid(makeRangeVar(remoterel->nspname,
                                              remoterel->relname, -1),
                                 lockmode, true);
        if (!OidIsValid(relid))
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("logical replication target relation \"%s.%s\" does not exist",
                            remoterel->nspname, remoterel->relname)));
        entry->localrel = table_open(relid, NoLock);
        entry->localreloid = relid;
 
        /* Check for supported relkind. */
        CheckSubscriptionRelkind(entry->localrel->rd_rel->relkind,
                                 remoterel->nspname, remoterel->relname);
 
        /*
         * Build the mapping of local attribute numbers to remote attribute
         * numbers and validate that we don't miss any replicated columns as
         * that would result in potentially unwanted data loss.
         */
        desc = RelationGetDescr(entry->localrel);
        oldctx = MemoryContextSwitchTo(LogicalRepRelMapContext);
        entry->attrmap = make_attrmap(desc->natts);
        MemoryContextSwitchTo(oldctx);
 
        /* check and report missing attrs, if any */
        missingatts = bms_add_range(NULL, 0, remoterel->natts - 1);
        for (i = 0; i < desc->natts; i++)
        {
            int         attnum;
            Form_pg_attribute attr = TupleDescAttr(desc, i);
 
            if (attr->attisdropped || attr->attgenerated)
            {
                entry->attrmap->attnums[i] = -1;
                continue;
            }
 
            attnum = logicalrep_rel_att_by_name(remoterel,
                                                NameStr(attr->attname));
 
            entry->attrmap->attnums[i] = attnum;
            if (attnum >= 0)
                missingatts = bms_del_member(missingatts, attnum);
        }
 
        logicalrep_report_missing_attrs(remoterel, missingatts);
 
        /* be tidy */
        bms_free(missingatts);
 
        /*
         * Set if the table's replica identity is enough to apply
         * update/delete.
         */
        logicalrep_rel_mark_updatable(entry);
 
        /*
         * Finding a usable index is an infrequent task. It occurs when an
         * operation is first performed on the relation, or after invalidation
         * of the relation cache entry (such as ANALYZE or CREATE/DROP index
         * on the relation).
         */
        entry->localindexoid = FindLogicalRepLocalIndex(entry->localrel, remoterel,
                                                        entry->attrmap);
 
        entry->localrelvalid = true;
    }
 
    if (entry->state != SUBREL_STATE_READY)
        entry->state = GetSubscriptionRelState(MySubscription->oid,
                                               entry->localreloid,
                                               &entry->statelsn);
 
    return entry;
}
 
/*
 * Close the previously opened logical relation.
 */
void
logicalrep_rel_close(LogicalRepRelMapEntry *rel, LOCKMODE lockmode)
{
    table_close(rel->localrel, lockmode);
    rel->localrel = NULL;
}
 
/*
 * Partition cache: look up partition LogicalRepRelMapEntry's
 *
 * Unlike relation map cache, this is keyed by partition OID, not remote
 * relation OID, because we only have to use this cache in the case where
 * partitions are not directly mapped to any remote relation, such as when
 * replication is occurring with one of their ancestors as target.
 */
 
/*
 * Relcache invalidation callback
 */
static void
logicalrep_partmap_invalidate_cb(Datum arg, Oid reloid)
{
    LogicalRepPartMapEntry *entry;
 
    /* Just to be sure. */
    if (LogicalRepPartMap == NULL)
        return;
 
    if (reloid != InvalidOid)
    {
        HASH_SEQ_STATUS status;
 
        hash_seq_init(&status, LogicalRepPartMap);
 
        /* TODO, use inverse lookup hashtable? */
        while ((entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
        {
            if (entry->relmapentry.localreloid == reloid)
            {
                entry->relmapentry.localrelvalid = false;
                hash_seq_term(&status);
                break;
            }
        }
    }
    else
    {
        /* invalidate all cache entries */
        HASH_SEQ_STATUS status;
 
        hash_seq_init(&status, LogicalRepPartMap);
 
        while ((entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
            entry->relmapentry.localrelvalid = false;
    }
}
 
/*
 * Reset the entries in the partition map that refer to remoterel.
 *
 * Called when new relation mapping is sent by the publisher to update our
 * expected view of incoming data from said publisher.
 *
 * Note that we don't update the remoterel information in the entry here,
 * we will update the information in logicalrep_partition_open to avoid
 * unnecessary work.
 */
void
logicalrep_partmap_reset_relmap(LogicalRepRelation *remoterel)
{
    HASH_SEQ_STATUS status;
    LogicalRepPartMapEntry *part_entry;
    LogicalRepRelMapEntry *entry;
 
    if (LogicalRepPartMap == NULL)
        return;
 
    hash_seq_init(&status, LogicalRepPartMap);
    while ((part_entry = (LogicalRepPartMapEntry *) hash_seq_search(&status)) != NULL)
    {
        entry = &part_entry->relmapentry;
 
        if (entry->remoterel.remoteid != remoterel->remoteid)
            continue;
 
        logicalrep_relmap_free_entry(entry);
 
        memset(entry, 0, sizeof(LogicalRepRelMapEntry));
    }
}
 
/*
 * Initialize the partition map cache.
 */
static void
logicalrep_partmap_init(void)
{
    HASHCTL     ctl;
 
    if (!LogicalRepPartMapContext)
        LogicalRepPartMapContext =
            AllocSetContextCreate(CacheMemoryContext,
                                  "LogicalRepPartMapContext",
                                  ALLOCSET_DEFAULT_SIZES);
 
    /* Initialize the relation hash table. */
    ctl.keysize = sizeof(Oid);  /* partition OID */
    ctl.entrysize = sizeof(LogicalRepPartMapEntry);
    ctl.hcxt = LogicalRepPartMapContext;
 
    LogicalRepPartMap = hash_create("logicalrep partition map cache", 64, &ctl,
                                    HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 
    /* Watch for invalidation events. */
    CacheRegisterRelcacheCallback(logicalrep_partmap_invalidate_cb,
                                  (Datum) 0);
}
 
/*
 * logicalrep_partition_open
 *
 * Returned entry reuses most of the values of the root table's entry, save
 * the attribute map, which can be different for the partition.  However,
 * we must physically copy all the data, in case the root table's entry
 * gets freed/rebuilt.
 *
 * Note there's no logicalrep_partition_close, because the caller closes the
 * component relation.
 */
LogicalRepRelMapEntry *
logicalrep_partition_open(LogicalRepRelMapEntry *root,
                          Relation partrel, AttrMap *map)
{
    LogicalRepRelMapEntry *entry;
    LogicalRepPartMapEntry *part_entry;
    LogicalRepRelation *remoterel = &root->remoterel;
    Oid         partOid = RelationGetRelid(partrel);
    AttrMap    *attrmap = root->attrmap;
    bool        found;
    MemoryContext oldctx;
 
    if (LogicalRepPartMap == NULL)
        logicalrep_partmap_init();
 
    /* Search for existing entry. */
    part_entry = (LogicalRepPartMapEntry *) hash_search(LogicalRepPartMap,
                                                        &partOid,
                                                        HASH_ENTER, &found);
 
    entry = &part_entry->relmapentry;
 
    /*
     * We must always overwrite entry->localrel with the latest partition
     * Relation pointer, because the Relation pointed to by the old value may
     * have been cleared after the caller would have closed the partition
     * relation after the last use of this entry.  Note that localrelvalid is
     * only updated by the relcache invalidation callback, so it may still be
     * true irrespective of whether the Relation pointed to by localrel has
     * been cleared or not.
     */
    if (found && entry->localrelvalid)
    {
        entry->localrel = partrel;
        return entry;
    }
 
    /* Switch to longer-lived context. */
    oldctx = MemoryContextSwitchTo(LogicalRepPartMapContext);
 
    if (!found)
    {
        memset(part_entry, 0, sizeof(LogicalRepPartMapEntry));
        part_entry->partoid = partOid;
    }
 
    /* Release the no-longer-useful attrmap, if any. */
    if (entry->attrmap)
    {
        free_attrmap(entry->attrmap);
        entry->attrmap = NULL;
    }
 
    if (!entry->remoterel.remoteid)
    {
        int         i;
 
        /* Remote relation is copied as-is from the root entry. */
        entry = &part_entry->relmapentry;
        entry->remoterel.remoteid = remoterel->remoteid;
        entry->remoterel.nspname = pstrdup(remoterel->nspname);
        entry->remoterel.relname = pstrdup(remoterel->relname);
        entry->remoterel.natts = remoterel->natts;
        entry->remoterel.attnames = palloc(remoterel->natts * sizeof(char *));
        entry->remoterel.atttyps = palloc(remoterel->natts * sizeof(Oid));
        for (i = 0; i < remoterel->natts; i++)
        {
            entry->remoterel.attnames[i] = pstrdup(remoterel->attnames[i]);
            entry->remoterel.atttyps[i] = remoterel->atttyps[i];
        }
        entry->remoterel.replident = remoterel->replident;
        entry->remoterel.attkeys = bms_copy(remoterel->attkeys);
    }
 
    entry->localrel = partrel;
    entry->localreloid = partOid;
 
    /*
     * If the partition's attributes don't match the root relation's, we'll
     * need to make a new attrmap which maps partition attribute numbers to
     * remoterel's, instead of the original which maps root relation's
     * attribute numbers to remoterel's.
     *
     * Note that 'map' which comes from the tuple routing data structure
     * contains 1-based attribute numbers (of the parent relation).  However,
     * the map in 'entry', a logical replication data structure, contains
     * 0-based attribute numbers (of the remote relation).
     */
    if (map)
    {
        AttrNumber  attno;
 
        entry->attrmap = make_attrmap(map->maplen);
        for (attno = 0; attno < entry->attrmap->maplen; attno++)
        {
            AttrNumber  root_attno = map->attnums[attno];
 
            /* 0 means it's a dropped attribute.  See comments atop AttrMap. */
            if (root_attno == 0)
                entry->attrmap->attnums[attno] = -1;
            else
                entry->attrmap->attnums[attno] = attrmap->attnums[root_attno - 1];
        }
    }
    else
    {
        /* Lacking copy_attmap, do this the hard way. */
        entry->attrmap = make_attrmap(attrmap->maplen);
        memcpy(entry->attrmap->attnums, attrmap->attnums,
               attrmap->maplen * sizeof(AttrNumber));
    }
 
    /* Set if the table's replica identity is enough to apply update/delete. */
    logicalrep_rel_mark_updatable(entry);
 
    /* state and statelsn are left set to 0. */
    MemoryContextSwitchTo(oldctx);
 
    /*
     * Finding a usable index is an infrequent task. It occurs when an
     * operation is first performed on the relation, or after invalidation of
     * the relation cache entry (such as ANALYZE or CREATE/DROP index on the
     * relation).
     *
     * We also prefer to run this code on the oldctx so that we do not leak
     * anything in the LogicalRepPartMapContext (hence CacheMemoryContext).
     */
    entry->localindexoid = FindLogicalRepLocalIndex(partrel, remoterel,
                                                    entry->attrmap);
 
    entry->localrelvalid = true;
 
    return entry;
}
 
/*
 * Returns the oid of an index that can be used by the apply worker to scan
 * the relation.
 *
 * We expect to call this function when REPLICA IDENTITY FULL is defined for
 * the remote relation.
 *
 * If no suitable index is found, returns InvalidOid.
 */
static Oid
FindUsableIndexForReplicaIdentityFull(Relation localrel, AttrMap *attrmap)
{
    List       *idxlist = RelationGetIndexList(localrel);
    ListCell   *lc;
 
    foreach(lc, idxlist)
    {
        Oid         idxoid = lfirst_oid(lc);
        bool        isUsableIdx;
        Relation    idxRel;
        IndexInfo  *idxInfo;
 
        idxRel = index_open(idxoid, AccessShareLock);
        idxInfo = BuildIndexInfo(idxRel);
        isUsableIdx = IsIndexUsableForReplicaIdentityFull(idxInfo, attrmap);
        index_close(idxRel, AccessShareLock);
 
        /* Return the first eligible index found */
        if (isUsableIdx)
            return idxoid;
    }
 
    return InvalidOid;
}
 
/*
 * Returns true if the index is usable for replica identity full.
 *
 * The index must be btree or hash, non-partial, and the leftmost field must be
 * a column (not an expression) that references the remote relation column. These
 * limitations help to keep the index scan similar to PK/RI index scans.
 *
 * attrmap is a map of local attributes to remote ones. We can consult this
 * map to check whether the local index attribute has a corresponding remote
 * attribute.
 *
 * Note that the limitations of index scans for replica identity full only
 * adheres to a subset of the limitations of PK/RI. For example, we support
 * columns that are marked as [NULL] or we are not interested in the [NOT
 * DEFERRABLE] aspect of constraints here. It works for us because we always
 * compare the tuples for non-PK/RI index scans. See
 * RelationFindReplTupleByIndex().
 *
 * The reasons why only Btree and Hash indexes can be considered as usable are:
 *
 * 1) Other index access methods don't have a fixed strategy for equality
 * operation. Refer get_equal_strategy_number_for_am().
 *
 * 2) For indexes other than PK and REPLICA IDENTITY, we need to match the
 * local and remote tuples. The equality routine tuples_equal() cannot accept
 * a datatype (e.g. point or box) that does not have a default operator class
 * for Btree or Hash.
 *
 * XXX: Note that BRIN and GIN indexes do not implement "amgettuple" which
 * will be used later to fetch the tuples. See RelationFindReplTupleByIndex().
 *
 * XXX: To support partial indexes, the required changes are likely to be larger.
 * If none of the tuples satisfy the expression for the index scan, we fall-back
 * to sequential execution, which might not be a good idea in some cases.
 */
bool
IsIndexUsableForReplicaIdentityFull(IndexInfo *indexInfo, AttrMap *attrmap)
{
    AttrNumber  keycol;
 
    /* Ensure that the index access method has a valid equal strategy */
    if (get_equal_strategy_number_for_am(indexInfo->ii_Am) == InvalidStrategy)
        return false;
 
    /* The index must not be a partial index */
    if (indexInfo->ii_Predicate != NIL)
        return false;
 
    Assert(indexInfo->ii_NumIndexAttrs >= 1);
 
    /* The leftmost index field must not be an expression */
    keycol = indexInfo->ii_IndexAttrNumbers[0];
    if (!AttributeNumberIsValid(keycol))
        return false;
 
    /*
     * And the leftmost index field must reference the remote relation column.
     * This is because if it doesn't, the sequential scan is favorable over
     * index scan in most cases.
     */
    if (attrmap->maplen <= AttrNumberGetAttrOffset(keycol) ||
        attrmap->attnums[AttrNumberGetAttrOffset(keycol)] < 0)
        return false;
 
#ifdef USE_ASSERT_CHECKING
    {
        IndexAmRoutine *amroutine;
 
        /* The given index access method must implement amgettuple. */
        amroutine = GetIndexAmRoutineByAmId(indexInfo->ii_Am, false);
        Assert(amroutine->amgettuple != NULL);
    }
#endif
 
    return true;
}
 
/*
 * Get replica identity index or if it is not defined a primary key.
 *
 * If neither is defined, returns InvalidOid
 */
Oid
GetRelationIdentityOrPK(Relation rel)
{
    Oid         idxoid;
 
    idxoid = RelationGetReplicaIndex(rel);
 
    if (!OidIsValid(idxoid))
        idxoid = RelationGetPrimaryKeyIndex(rel);
 
    return idxoid;
}
 
/*
 * Returns the index oid if we can use an index for subscriber. Otherwise,
 * returns InvalidOid.
 */
static Oid
FindLogicalRepLocalIndex(Relation localrel, LogicalRepRelation *remoterel,
                         AttrMap *attrMap)
{
    Oid         idxoid;
 
    /*
     * We never need index oid for partitioned tables, always rely on leaf
     * partition's index.
     */
    if (localrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        return InvalidOid;
 
    /*
     * Simple case, we already have a primary key or a replica identity index.
     */
    idxoid = GetRelationIdentityOrPK(localrel);
    if (OidIsValid(idxoid))
        return idxoid;
 
    if (remoterel->replident == REPLICA_IDENTITY_FULL)
    {
        /*
         * We are looking for one more opportunity for using an index. If
         * there are any indexes defined on the local relation, try to pick a
         * suitable index.
         *
         * The index selection safely assumes that all the columns are going
         * to be available for the index scan given that remote relation has
         * replica identity full.
         *
         * Note that we are not using the planner to find the cheapest method
         * to scan the relation as that would require us to either use lower
         * level planner functions which would be a maintenance burden in the
         * long run or use the full-fledged planner which could cause
         * overhead.
         */
        return FindUsableIndexForReplicaIdentityFull(localrel, attrMap);
    }
 
    return InvalidOid;
}