pg_subscription.c

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/*-------------------------------------------------------------------------
 *
 * pg_subscription.c
 *      replication subscriptions
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *      src/backend/catalog/pg_subscription.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "miscadmin.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/xact.h"

#include "catalog/indexing.h"
#include "catalog/pg_type.h"
#include "catalog/pg_subscription.h"
#include "catalog/pg_subscription_rel.h"

#include "nodes/makefuncs.h"

#include "storage/lmgr.h"

#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/pg_lsn.h"
#include "utils/rel.h"
#include "utils/syscache.h"


static List *textarray_to_stringlist(ArrayType *textarray);

/*
 * Fetch the subscription from the syscache.
 */
Subscription *
GetSubscription(Oid subid, bool missing_ok)
{
    HeapTuple   tup;
    Subscription *sub;
    Form_pg_subscription subform;
    Datum       datum;
    bool        isnull;

    tup = SearchSysCache1(SUBSCRIPTIONOID, ObjectIdGetDatum(subid));

    if (!HeapTupleIsValid(tup))
    {
        if (missing_ok)
            return NULL;

        elog(ERROR, "cache lookup failed for subscription %u", subid);
    }

    subform = (Form_pg_subscription) GETSTRUCT(tup);

    sub = (Subscription *) palloc(sizeof(Subscription));
    sub->oid = subid;
    sub->dbid = subform->subdbid;
    sub->name = pstrdup(NameStr(subform->subname));
    sub->owner = subform->subowner;
    sub->enabled = subform->subenabled;

    /* Get conninfo */
    datum = SysCacheGetAttr(SUBSCRIPTIONOID,
                            tup,
                            Anum_pg_subscription_subconninfo,
                            &isnull);
    Assert(!isnull);
    sub->conninfo = TextDatumGetCString(datum);

    /* Get slotname */
    datum = SysCacheGetAttr(SUBSCRIPTIONOID,
                            tup,
                            Anum_pg_subscription_subslotname,
                            &isnull);
    if (!isnull)
        sub->slotname = pstrdup(NameStr(*DatumGetName(datum)));
    else
        sub->slotname = NULL;

    /* Get synccommit */
    datum = SysCacheGetAttr(SUBSCRIPTIONOID,
                            tup,
                            Anum_pg_subscription_subsynccommit,
                            &isnull);
    Assert(!isnull);
    sub->synccommit = TextDatumGetCString(datum);

    /* Get publications */
    datum = SysCacheGetAttr(SUBSCRIPTIONOID,
                            tup,
                            Anum_pg_subscription_subpublications,
                            &isnull);
    Assert(!isnull);
    sub->publications = textarray_to_stringlist(DatumGetArrayTypeP(datum));

    ReleaseSysCache(tup);

    return sub;
}

/*
 * Return number of subscriptions defined in given database.
 * Used by dropdb() to check if database can indeed be dropped.
 */
int
CountDBSubscriptions(Oid dbid)
{
    int         nsubs = 0;
    Relation    rel;
    ScanKeyData scankey;
    SysScanDesc scan;
    HeapTuple   tup;

    rel = heap_open(SubscriptionRelationId, RowExclusiveLock);

    ScanKeyInit(&scankey,
                Anum_pg_subscription_subdbid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(dbid));

    scan = systable_beginscan(rel, InvalidOid, false,
                              NULL, 1, &scankey);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
        nsubs++;

    systable_endscan(scan);

    heap_close(rel, NoLock);

    return nsubs;
}

/*
 * Free memory allocated by subscription struct.
 */
void
FreeSubscription(Subscription *sub)
{
    pfree(sub->name);
    pfree(sub->conninfo);
    if (sub->slotname)
        pfree(sub->slotname);
    list_free_deep(sub->publications);
    pfree(sub);
}

/*
 * get_subscription_oid - given a subscription name, look up the OID
 *
 * If missing_ok is false, throw an error if name not found.  If true, just
 * return InvalidOid.
 */
Oid
get_subscription_oid(const char *subname, bool missing_ok)
{
    Oid         oid;

    oid = GetSysCacheOid2(SUBSCRIPTIONNAME, MyDatabaseId,
                          CStringGetDatum(subname));
    if (!OidIsValid(oid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("subscription \"%s\" does not exist", subname)));
    return oid;
}

/*
 * get_subscription_name - given a subscription OID, look up the name
 */
char *
get_subscription_name(Oid subid)
{
    HeapTuple   tup;
    char       *subname;
    Form_pg_subscription subform;

    tup = SearchSysCache1(SUBSCRIPTIONOID, ObjectIdGetDatum(subid));

    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for subscription %u", subid);

    subform = (Form_pg_subscription) GETSTRUCT(tup);
    subname = pstrdup(NameStr(subform->subname));

    ReleaseSysCache(tup);

    return subname;
}

/*
 * Convert text array to list of strings.
 *
 * Note: the resulting list of strings is pallocated here.
 */
static List *
textarray_to_stringlist(ArrayType *textarray)
{
    Datum      *elems;
    int         nelems,
                i;
    List       *res = NIL;

    deconstruct_array(textarray,
                      TEXTOID, -1, false, 'i',
                      &elems, NULL, &nelems);

    if (nelems == 0)
        return NIL;

    for (i = 0; i < nelems; i++)
        res = lappend(res, makeString(TextDatumGetCString(elems[i])));

    return res;
}

/*
 * Set the state of a subscription table.
 *
 * If update_only is true and the record for given table doesn't exist, do
 * nothing.  This can be used to avoid inserting a new record that was deleted
 * by someone else.  Generally, subscription DDL commands should use false,
 * workers should use true.
 *
 * The insert-or-update logic in this function is not concurrency safe so it
 * might raise an error in rare circumstances.  But if we took a stronger lock
 * such as ShareRowExclusiveLock, we would risk more deadlocks.
 */
Oid
SetSubscriptionRelState(Oid subid, Oid relid, char state,
                        XLogRecPtr sublsn, bool update_only)
{
    Relation    rel;
    HeapTuple   tup;
    Oid         subrelid = InvalidOid;
    bool        nulls[Natts_pg_subscription_rel];
    Datum       values[Natts_pg_subscription_rel];

    LockSharedObject(SubscriptionRelationId, subid, 0, AccessShareLock);

    rel = heap_open(SubscriptionRelRelationId, RowExclusiveLock);

    /* Try finding existing mapping. */
    tup = SearchSysCacheCopy2(SUBSCRIPTIONRELMAP,
                              ObjectIdGetDatum(relid),
                              ObjectIdGetDatum(subid));

    /*
     * If the record for given table does not exist yet create new record,
     * otherwise update the existing one.
     */
    if (!HeapTupleIsValid(tup) && !update_only)
    {
        /* Form the tuple. */
        memset(values, 0, sizeof(values));
        memset(nulls, false, sizeof(nulls));
        values[Anum_pg_subscription_rel_srsubid - 1] = ObjectIdGetDatum(subid);
        values[Anum_pg_subscription_rel_srrelid - 1] = ObjectIdGetDatum(relid);
        values[Anum_pg_subscription_rel_srsubstate - 1] = CharGetDatum(state);
        if (sublsn != InvalidXLogRecPtr)
            values[Anum_pg_subscription_rel_srsublsn - 1] = LSNGetDatum(sublsn);
        else
            nulls[Anum_pg_subscription_rel_srsublsn - 1] = true;

        tup = heap_form_tuple(RelationGetDescr(rel), values, nulls);

        /* Insert tuple into catalog. */
        subrelid = CatalogTupleInsert(rel, tup);

        heap_freetuple(tup);
    }
    else if (HeapTupleIsValid(tup))
    {
        bool        replaces[Natts_pg_subscription_rel];

        /* Update the tuple. */
        memset(values, 0, sizeof(values));
        memset(nulls, false, sizeof(nulls));
        memset(replaces, false, sizeof(replaces));

        replaces[Anum_pg_subscription_rel_srsubstate - 1] = true;
        values[Anum_pg_subscription_rel_srsubstate - 1] = CharGetDatum(state);

        replaces[Anum_pg_subscription_rel_srsublsn - 1] = true;
        if (sublsn != InvalidXLogRecPtr)
            values[Anum_pg_subscription_rel_srsublsn - 1] = LSNGetDatum(sublsn);
        else
            nulls[Anum_pg_subscription_rel_srsublsn - 1] = true;

        tup = heap_modify_tuple(tup, RelationGetDescr(rel), values, nulls,
                                replaces);

        /* Update the catalog. */
        CatalogTupleUpdate(rel, &tup->t_self, tup);

        subrelid = HeapTupleGetOid(tup);
    }

    /* Cleanup. */
    heap_close(rel, NoLock);

    return subrelid;
}

/*
 * Get state of subscription table.
 *
 * Returns SUBREL_STATE_UNKNOWN when not found and missing_ok is true.
 */
char
GetSubscriptionRelState(Oid subid, Oid relid, XLogRecPtr *sublsn,
                        bool missing_ok)
{
    Relation    rel;
    HeapTuple   tup;
    char        substate;
    bool        isnull;
    Datum       d;

    rel = heap_open(SubscriptionRelRelationId, AccessShareLock);

    /* Try finding the mapping. */
    tup = SearchSysCache2(SUBSCRIPTIONRELMAP,
                          ObjectIdGetDatum(relid),
                          ObjectIdGetDatum(subid));

    if (!HeapTupleIsValid(tup))
    {
        if (missing_ok)
        {
            heap_close(rel, AccessShareLock);
            *sublsn = InvalidXLogRecPtr;
            return SUBREL_STATE_UNKNOWN;
        }

        elog(ERROR, "subscription table %u in subscription %u does not exist",
             relid, subid);
    }

    /* Get the state. */
    d = SysCacheGetAttr(SUBSCRIPTIONRELMAP, tup,
                        Anum_pg_subscription_rel_srsubstate, &isnull);
    Assert(!isnull);
    substate = DatumGetChar(d);
    d = SysCacheGetAttr(SUBSCRIPTIONRELMAP, tup,
                        Anum_pg_subscription_rel_srsublsn, &isnull);
    if (isnull)
        *sublsn = InvalidXLogRecPtr;
    else
        *sublsn = DatumGetLSN(d);

    /* Cleanup */
    ReleaseSysCache(tup);
    heap_close(rel, AccessShareLock);

    return substate;
}

/*
 * Drop subscription relation mapping. These can be for a particular
 * subscription, or for a particular relation, or both.
 */
void
RemoveSubscriptionRel(Oid subid, Oid relid)
{
    Relation    rel;
    HeapScanDesc scan;
    ScanKeyData skey[2];
    HeapTuple   tup;
    int         nkeys = 0;

    rel = heap_open(SubscriptionRelRelationId, RowExclusiveLock);

    if (OidIsValid(subid))
    {
        ScanKeyInit(&skey[nkeys++],
                    Anum_pg_subscription_rel_srsubid,
                    BTEqualStrategyNumber,
                    F_OIDEQ,
                    ObjectIdGetDatum(subid));
    }

    if (OidIsValid(relid))
    {
        ScanKeyInit(&skey[nkeys++],
                    Anum_pg_subscription_rel_srrelid,
                    BTEqualStrategyNumber,
                    F_OIDEQ,
                    ObjectIdGetDatum(relid));
    }

    /* Do the search and delete what we found. */
    scan = heap_beginscan_catalog(rel, nkeys, skey);
    while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
    {
        CatalogTupleDelete(rel, &tup->t_self);
    }
    heap_endscan(scan);

    heap_close(rel, RowExclusiveLock);
}


/*
 * Get all relations for subscription.
 *
 * Returned list is palloc'ed in current memory context.
 */
List *
GetSubscriptionRelations(Oid subid)
{
    List       *res = NIL;
    Relation    rel;
    HeapTuple   tup;
    int         nkeys = 0;
    ScanKeyData skey[2];
    SysScanDesc scan;

    rel = heap_open(SubscriptionRelRelationId, AccessShareLock);

    ScanKeyInit(&skey[nkeys++],
                Anum_pg_subscription_rel_srsubid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(subid));

    scan = systable_beginscan(rel, InvalidOid, false,
                              NULL, nkeys, skey);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_subscription_rel subrel;
        SubscriptionRelState *relstate;

        subrel = (Form_pg_subscription_rel) GETSTRUCT(tup);

        relstate = (SubscriptionRelState *) palloc(sizeof(SubscriptionRelState));
        relstate->relid = subrel->srrelid;
        relstate->state = subrel->srsubstate;
        relstate->lsn = subrel->srsublsn;

        res = lappend(res, relstate);
    }

    /* Cleanup */
    systable_endscan(scan);
    heap_close(rel, AccessShareLock);

    return res;
}

/*
 * Get all relations for subscription that are not in a ready state.
 *
 * Returned list is palloc'ed in current memory context.
 */
List *
GetSubscriptionNotReadyRelations(Oid subid)
{
    List       *res = NIL;
    Relation    rel;
    HeapTuple   tup;
    int         nkeys = 0;
    ScanKeyData skey[2];
    SysScanDesc scan;

    rel = heap_open(SubscriptionRelRelationId, AccessShareLock);

    ScanKeyInit(&skey[nkeys++],
                Anum_pg_subscription_rel_srsubid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(subid));

    ScanKeyInit(&skey[nkeys++],
                Anum_pg_subscription_rel_srsubstate,
                BTEqualStrategyNumber, F_CHARNE,
                CharGetDatum(SUBREL_STATE_READY));

    scan = systable_beginscan(rel, InvalidOid, false,
                              NULL, nkeys, skey);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_subscription_rel subrel;
        SubscriptionRelState *relstate;

        subrel = (Form_pg_subscription_rel) GETSTRUCT(tup);

        relstate = (SubscriptionRelState *) palloc(sizeof(SubscriptionRelState));
        relstate->relid = subrel->srrelid;
        relstate->state = subrel->srsubstate;
        relstate->lsn = subrel->srsublsn;

        res = lappend(res, relstate);
    }

    /* Cleanup */
    systable_endscan(scan);
    heap_close(rel, AccessShareLock);

    return res;
}