subscriptioncmds.c

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/*-------------------------------------------------------------------------
 *
 * subscriptioncmds.c
 *      subscription catalog manipulation functions
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *      subscriptioncmds.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "access/table.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/objectaddress.h"
#include "catalog/pg_subscription.h"
#include "catalog/pg_subscription_rel.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "commands/event_trigger.h"
#include "commands/subscriptioncmds.h"
#include "executor/executor.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "replication/logicallauncher.h"
#include "replication/origin.h"
#include "replication/slot.h"
#include "replication/walreceiver.h"
#include "replication/walsender.h"
#include "replication/worker_internal.h"
#include "storage/lmgr.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"

/*
 * Options that can be specified by the user in CREATE/ALTER SUBSCRIPTION
 * command.
 */
#define SUBOPT_CONNECT              0x00000001
#define SUBOPT_ENABLED              0x00000002
#define SUBOPT_CREATE_SLOT          0x00000004
#define SUBOPT_SLOT_NAME            0x00000008
#define SUBOPT_COPY_DATA            0x00000010
#define SUBOPT_SYNCHRONOUS_COMMIT   0x00000020
#define SUBOPT_REFRESH              0x00000040
#define SUBOPT_BINARY               0x00000080
#define SUBOPT_STREAMING            0x00000100
#define SUBOPT_TWOPHASE_COMMIT      0x00000200

/* check if the 'val' has 'bits' set */
#define IsSet(val, bits)  (((val) & (bits)) == (bits))

/*
 * Structure to hold a bitmap representing the user-provided CREATE/ALTER
 * SUBSCRIPTION command options and the parsed/default values of each of them.
 */
typedef struct SubOpts
{
    bits32      specified_opts;
    char       *slot_name;
    char       *synchronous_commit;
    bool        connect;
    bool        enabled;
    bool        create_slot;
    bool        copy_data;
    bool        refresh;
    bool        binary;
    bool        streaming;
    bool        twophase;
} SubOpts;

static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
static void check_duplicates_in_publist(List *publist, Datum *datums);
static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);


/*
 * Common option parsing function for CREATE and ALTER SUBSCRIPTION commands.
 *
 * Since not all options can be specified in both commands, this function
 * will report an error if mutually exclusive options are specified.
 *
 * Caller is expected to have cleared 'opts'.
 */
static void
parse_subscription_options(ParseState *pstate, List *stmt_options,
                           bits32 supported_opts, SubOpts *opts)
{
    ListCell   *lc;

    /* caller must expect some option */
    Assert(supported_opts != 0);

    /* If connect option is supported, these others also need to be. */
    Assert(!IsSet(supported_opts, SUBOPT_CONNECT) ||
           IsSet(supported_opts, SUBOPT_ENABLED | SUBOPT_CREATE_SLOT |
                 SUBOPT_COPY_DATA));

    /* Set default values for the boolean supported options. */
    if (IsSet(supported_opts, SUBOPT_CONNECT))
        opts->connect = true;
    if (IsSet(supported_opts, SUBOPT_ENABLED))
        opts->enabled = true;
    if (IsSet(supported_opts, SUBOPT_CREATE_SLOT))
        opts->create_slot = true;
    if (IsSet(supported_opts, SUBOPT_COPY_DATA))
        opts->copy_data = true;
    if (IsSet(supported_opts, SUBOPT_REFRESH))
        opts->refresh = true;
    if (IsSet(supported_opts, SUBOPT_BINARY))
        opts->binary = false;
    if (IsSet(supported_opts, SUBOPT_STREAMING))
        opts->streaming = false;
    if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
        opts->twophase = false;

    /* Parse options */
    foreach(lc, stmt_options)
    {
        DefElem    *defel = (DefElem *) lfirst(lc);

        if (IsSet(supported_opts, SUBOPT_CONNECT) &&
            strcmp(defel->defname, "connect") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_CONNECT))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_CONNECT;
            opts->connect = defGetBoolean(defel);
        }
        else if (IsSet(supported_opts, SUBOPT_ENABLED) &&
                 strcmp(defel->defname, "enabled") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_ENABLED))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_ENABLED;
            opts->enabled = defGetBoolean(defel);
        }
        else if (IsSet(supported_opts, SUBOPT_CREATE_SLOT) &&
                 strcmp(defel->defname, "create_slot") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_CREATE_SLOT))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_CREATE_SLOT;
            opts->create_slot = defGetBoolean(defel);
        }
        else if (IsSet(supported_opts, SUBOPT_SLOT_NAME) &&
                 strcmp(defel->defname, "slot_name") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_SLOT_NAME))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_SLOT_NAME;
            opts->slot_name = defGetString(defel);

            /* Setting slot_name = NONE is treated as no slot name. */
            if (strcmp(opts->slot_name, "none") == 0)
                opts->slot_name = NULL;
            else
                ReplicationSlotValidateName(opts->slot_name, ERROR);
        }
        else if (IsSet(supported_opts, SUBOPT_COPY_DATA) &&
                 strcmp(defel->defname, "copy_data") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_COPY_DATA))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_COPY_DATA;
            opts->copy_data = defGetBoolean(defel);
        }
        else if (IsSet(supported_opts, SUBOPT_SYNCHRONOUS_COMMIT) &&
                 strcmp(defel->defname, "synchronous_commit") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_SYNCHRONOUS_COMMIT))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_SYNCHRONOUS_COMMIT;
            opts->synchronous_commit = defGetString(defel);

            /* Test if the given value is valid for synchronous_commit GUC. */
            (void) set_config_option("synchronous_commit", opts->synchronous_commit,
                                     PGC_BACKEND, PGC_S_TEST, GUC_ACTION_SET,
                                     false, 0, false);
        }
        else if (IsSet(supported_opts, SUBOPT_REFRESH) &&
                 strcmp(defel->defname, "refresh") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_REFRESH))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_REFRESH;
            opts->refresh = defGetBoolean(defel);
        }
        else if (IsSet(supported_opts, SUBOPT_BINARY) &&
                 strcmp(defel->defname, "binary") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_BINARY))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_BINARY;
            opts->binary = defGetBoolean(defel);
        }
        else if (IsSet(supported_opts, SUBOPT_STREAMING) &&
                 strcmp(defel->defname, "streaming") == 0)
        {
            if (IsSet(opts->specified_opts, SUBOPT_STREAMING))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_STREAMING;
            opts->streaming = defGetBoolean(defel);
        }
        else if (strcmp(defel->defname, "two_phase") == 0)
        {
            /*
             * Do not allow toggling of two_phase option. Doing so could cause
             * missing of transactions and lead to an inconsistent replica.
             * See comments atop worker.c
             *
             * Note: Unsupported twophase indicates that this call originated
             * from AlterSubscription.
             */
            if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));

            if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
                errorConflictingDefElem(defel, pstate);

            opts->specified_opts |= SUBOPT_TWOPHASE_COMMIT;
            opts->twophase = defGetBoolean(defel);
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
    }

    /*
     * We've been explicitly asked to not connect, that requires some
     * additional processing.
     */
    if (!opts->connect && IsSet(supported_opts, SUBOPT_CONNECT))
    {
        /* Check for incompatible options from the user. */
        if (opts->enabled &&
            IsSet(supported_opts, SUBOPT_ENABLED) &&
            IsSet(opts->specified_opts, SUBOPT_ENABLED))
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
            /*- translator: both %s are strings of the form "option = value" */
                     errmsg("%s and %s are mutually exclusive options",
                            "connect = false", "enabled = true")));

        if (opts->create_slot &&
            IsSet(supported_opts, SUBOPT_CREATE_SLOT) &&
            IsSet(opts->specified_opts, SUBOPT_CREATE_SLOT))
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("%s and %s are mutually exclusive options",
                            "connect = false", "create_slot = true")));

        if (opts->copy_data &&
            IsSet(supported_opts, SUBOPT_COPY_DATA) &&
            IsSet(opts->specified_opts, SUBOPT_COPY_DATA))
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("%s and %s are mutually exclusive options",
                            "connect = false", "copy_data = true")));

        /* Change the defaults of other options. */
        opts->enabled = false;
        opts->create_slot = false;
        opts->copy_data = false;
    }

    /*
     * Do additional checking for disallowed combination when slot_name = NONE
     * was used.
     */
    if (!opts->slot_name &&
        IsSet(supported_opts, SUBOPT_SLOT_NAME) &&
        IsSet(opts->specified_opts, SUBOPT_SLOT_NAME))
    {
        if (opts->enabled &&
            IsSet(supported_opts, SUBOPT_ENABLED) &&
            IsSet(opts->specified_opts, SUBOPT_ENABLED))
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
            /*- translator: both %s are strings of the form "option = value" */
                     errmsg("%s and %s are mutually exclusive options",
                            "slot_name = NONE", "enabled = true")));

        if (opts->create_slot &&
            IsSet(supported_opts, SUBOPT_CREATE_SLOT) &&
            IsSet(opts->specified_opts, SUBOPT_CREATE_SLOT))
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
            /*- translator: both %s are strings of the form "option = value" */
                     errmsg("%s and %s are mutually exclusive options",
                            "slot_name = NONE", "create_slot = true")));

        if (opts->enabled &&
            IsSet(supported_opts, SUBOPT_ENABLED) &&
            !IsSet(opts->specified_opts, SUBOPT_ENABLED))
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
            /*- translator: both %s are strings of the form "option = value" */
                     errmsg("subscription with %s must also set %s",
                            "slot_name = NONE", "enabled = false")));

        if (opts->create_slot &&
            IsSet(supported_opts, SUBOPT_CREATE_SLOT) &&
            !IsSet(opts->specified_opts, SUBOPT_CREATE_SLOT))
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
            /*- translator: both %s are strings of the form "option = value" */
                     errmsg("subscription with %s must also set %s",
                            "slot_name = NONE", "create_slot = false")));
    }
}

/*
 * Auxiliary function to build a text array out of a list of String nodes.
 */
static Datum
publicationListToArray(List *publist)
{
    ArrayType  *arr;
    Datum      *datums;
    MemoryContext memcxt;
    MemoryContext oldcxt;

    /* Create memory context for temporary allocations. */
    memcxt = AllocSetContextCreate(CurrentMemoryContext,
                                   "publicationListToArray to array",
                                   ALLOCSET_DEFAULT_SIZES);
    oldcxt = MemoryContextSwitchTo(memcxt);

    datums = (Datum *) palloc(sizeof(Datum) * list_length(publist));

    check_duplicates_in_publist(publist, datums);

    MemoryContextSwitchTo(oldcxt);

    arr = construct_array(datums, list_length(publist),
                          TEXTOID, -1, false, TYPALIGN_INT);

    MemoryContextDelete(memcxt);

    return PointerGetDatum(arr);
}

/*
 * Create new subscription.
 */
ObjectAddress
CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
                   bool isTopLevel)
{
    Relation    rel;
    ObjectAddress myself;
    Oid         subid;
    bool        nulls[Natts_pg_subscription];
    Datum       values[Natts_pg_subscription];
    Oid         owner = GetUserId();
    HeapTuple   tup;
    char       *conninfo;
    char        originname[NAMEDATALEN];
    List       *publications;
    bits32      supported_opts;
    SubOpts     opts = {0};

    /*
     * Parse and check options.
     *
     * Connection and publication should not be specified here.
     */
    supported_opts = (SUBOPT_CONNECT | SUBOPT_ENABLED | SUBOPT_CREATE_SLOT |
                      SUBOPT_SLOT_NAME | SUBOPT_COPY_DATA |
                      SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
                      SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT);
    parse_subscription_options(pstate, stmt->options, supported_opts, &opts);

    /*
     * Since creating a replication slot is not transactional, rolling back
     * the transaction leaves the created replication slot.  So we cannot run
     * CREATE SUBSCRIPTION inside a transaction block if creating a
     * replication slot.
     */
    if (opts.create_slot)
        PreventInTransactionBlock(isTopLevel, "CREATE SUBSCRIPTION ... WITH (create_slot = true)");

    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to create subscriptions")));

    /*
     * If built with appropriate switch, whine when regression-testing
     * conventions for subscription names are violated.
     */
#ifdef ENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
    if (strncmp(stmt->subname, "regress_", 8) != 0)
        elog(WARNING, "subscriptions created by regression test cases should have names starting with \"regress_\"");
#endif

    rel = table_open(SubscriptionRelationId, RowExclusiveLock);

    /* Check if name is used */
    subid = GetSysCacheOid2(SUBSCRIPTIONNAME, Anum_pg_subscription_oid,
                            MyDatabaseId, CStringGetDatum(stmt->subname));
    if (OidIsValid(subid))
    {
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("subscription \"%s\" already exists",
                        stmt->subname)));
    }

    if (!IsSet(opts.specified_opts, SUBOPT_SLOT_NAME) &&
        opts.slot_name == NULL)
        opts.slot_name = stmt->subname;

    /* The default for synchronous_commit of subscriptions is off. */
    if (opts.synchronous_commit == NULL)
        opts.synchronous_commit = "off";

    conninfo = stmt->conninfo;
    publications = stmt->publication;

    /* Load the library providing us libpq calls. */
    load_file("libpqwalreceiver", false);

    /* Check the connection info string. */
    walrcv_check_conninfo(conninfo);

    /* Everything ok, form a new tuple. */
    memset(values, 0, sizeof(values));
    memset(nulls, false, sizeof(nulls));

    subid = GetNewOidWithIndex(rel, SubscriptionObjectIndexId,
                               Anum_pg_subscription_oid);
    values[Anum_pg_subscription_oid - 1] = ObjectIdGetDatum(subid);
    values[Anum_pg_subscription_subdbid - 1] = ObjectIdGetDatum(MyDatabaseId);
    values[Anum_pg_subscription_subname - 1] =
        DirectFunctionCall1(namein, CStringGetDatum(stmt->subname));
    values[Anum_pg_subscription_subowner - 1] = ObjectIdGetDatum(owner);
    values[Anum_pg_subscription_subenabled - 1] = BoolGetDatum(opts.enabled);
    values[Anum_pg_subscription_subbinary - 1] = BoolGetDatum(opts.binary);
    values[Anum_pg_subscription_substream - 1] = BoolGetDatum(opts.streaming);
    values[Anum_pg_subscription_subtwophasestate - 1] =
        CharGetDatum(opts.twophase ?
                     LOGICALREP_TWOPHASE_STATE_PENDING :
                     LOGICALREP_TWOPHASE_STATE_DISABLED);
    values[Anum_pg_subscription_subconninfo - 1] =
        CStringGetTextDatum(conninfo);
    if (opts.slot_name)
        values[Anum_pg_subscription_subslotname - 1] =
            DirectFunctionCall1(namein, CStringGetDatum(opts.slot_name));
    else
        nulls[Anum_pg_subscription_subslotname - 1] = true;
    values[Anum_pg_subscription_subsynccommit - 1] =
        CStringGetTextDatum(opts.synchronous_commit);
    values[Anum_pg_subscription_subpublications - 1] =
        publicationListToArray(publications);

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

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

    recordDependencyOnOwner(SubscriptionRelationId, subid, owner);

    snprintf(originname, sizeof(originname), "pg_%u", subid);
    replorigin_create(originname);

    /*
     * Connect to remote side to execute requested commands and fetch table
     * info.
     */
    if (opts.connect)
    {
        char       *err;
        WalReceiverConn *wrconn;
        List       *tables;
        ListCell   *lc;
        char        table_state;

        /* Try to connect to the publisher. */
        wrconn = walrcv_connect(conninfo, true, stmt->subname, &err);
        if (!wrconn)
            ereport(ERROR,
                    (errcode(ERRCODE_CONNECTION_FAILURE),
                     errmsg("could not connect to the publisher: %s", err)));

        PG_TRY();
        {
            /*
             * Set sync state based on if we were asked to do data copy or
             * not.
             */
            table_state = opts.copy_data ? SUBREL_STATE_INIT : SUBREL_STATE_READY;

            /*
             * Get the table list from publisher and build local table status
             * info.
             */
            tables = fetch_table_list(wrconn, publications);
            foreach(lc, tables)
            {
                RangeVar   *rv = (RangeVar *) lfirst(lc);
                Oid         relid;

                relid = RangeVarGetRelid(rv, AccessShareLock, false);

                /* Check for supported relkind. */
                CheckSubscriptionRelkind(get_rel_relkind(relid),
                                         rv->schemaname, rv->relname);

                AddSubscriptionRelState(subid, relid, table_state,
                                        InvalidXLogRecPtr);
            }

            /*
             * If requested, create permanent slot for the subscription. We
             * won't use the initial snapshot for anything, so no need to
             * export it.
             */
            if (opts.create_slot)
            {
                bool        twophase_enabled = false;

                Assert(opts.slot_name);

                /*
                 * Even if two_phase is set, don't create the slot with
                 * two-phase enabled. Will enable it once all the tables are
                 * synced and ready. This avoids race-conditions like prepared
                 * transactions being skipped due to changes not being applied
                 * due to checks in should_apply_changes_for_rel() when
                 * tablesync for the corresponding tables are in progress. See
                 * comments atop worker.c.
                 *
                 * Note that if tables were specified but copy_data is false
                 * then it is safe to enable two_phase up-front because those
                 * tables are already initially in READY state. When the
                 * subscription has no tables, we leave the twophase state as
                 * PENDING, to allow ALTER SUBSCRIPTION ... REFRESH
                 * PUBLICATION to work.
                 */
                if (opts.twophase && !opts.copy_data && tables != NIL)
                    twophase_enabled = true;

                walrcv_create_slot(wrconn, opts.slot_name, false, twophase_enabled,
                                   CRS_NOEXPORT_SNAPSHOT, NULL);

                if (twophase_enabled)
                    UpdateTwoPhaseState(subid, LOGICALREP_TWOPHASE_STATE_ENABLED);

                ereport(NOTICE,
                        (errmsg("created replication slot \"%s\" on publisher",
                                opts.slot_name)));
            }
        }
        PG_FINALLY();
        {
            walrcv_disconnect(wrconn);
        }
        PG_END_TRY();
    }
    else
        ereport(WARNING,
        /* translator: %s is an SQL ALTER statement */
                (errmsg("tables were not subscribed, you will have to run %s to subscribe the tables",
                        "ALTER SUBSCRIPTION ... REFRESH PUBLICATION")));

    table_close(rel, RowExclusiveLock);

    if (opts.enabled)
        ApplyLauncherWakeupAtCommit();

    ObjectAddressSet(myself, SubscriptionRelationId, subid);

    InvokeObjectPostCreateHook(SubscriptionRelationId, subid, 0);

    return myself;
}

static void
AlterSubscription_refresh(Subscription *sub, bool copy_data)
{
    char       *err;
    List       *pubrel_names;
    List       *subrel_states;
    Oid        *subrel_local_oids;
    Oid        *pubrel_local_oids;
    ListCell   *lc;
    int         off;
    int         remove_rel_len;
    Relation    rel = NULL;
    typedef struct SubRemoveRels
    {
        Oid         relid;
        char        state;
    } SubRemoveRels;
    SubRemoveRels *sub_remove_rels;
    WalReceiverConn *wrconn;

    /* Load the library providing us libpq calls. */
    load_file("libpqwalreceiver", false);

    /* Try to connect to the publisher. */
    wrconn = walrcv_connect(sub->conninfo, true, sub->name, &err);
    if (!wrconn)
        ereport(ERROR,
                (errcode(ERRCODE_CONNECTION_FAILURE),
                 errmsg("could not connect to the publisher: %s", err)));

    PG_TRY();
    {
        /* Get the table list from publisher. */
        pubrel_names = fetch_table_list(wrconn, sub->publications);

        /* Get local table list. */
        subrel_states = GetSubscriptionRelations(sub->oid);

        /*
         * Build qsorted array of local table oids for faster lookup. This can
         * potentially contain all tables in the database so speed of lookup
         * is important.
         */
        subrel_local_oids = palloc(list_length(subrel_states) * sizeof(Oid));
        off = 0;
        foreach(lc, subrel_states)
        {
            SubscriptionRelState *relstate = (SubscriptionRelState *) lfirst(lc);

            subrel_local_oids[off++] = relstate->relid;
        }
        qsort(subrel_local_oids, list_length(subrel_states),
              sizeof(Oid), oid_cmp);

        /*
         * Rels that we want to remove from subscription and drop any slots
         * and origins corresponding to them.
         */
        sub_remove_rels = palloc(list_length(subrel_states) * sizeof(SubRemoveRels));

        /*
         * Walk over the remote tables and try to match them to locally known
         * tables. If the table is not known locally create a new state for
         * it.
         *
         * Also builds array of local oids of remote tables for the next step.
         */
        off = 0;
        pubrel_local_oids = palloc(list_length(pubrel_names) * sizeof(Oid));

        foreach(lc, pubrel_names)
        {
            RangeVar   *rv = (RangeVar *) lfirst(lc);
            Oid         relid;

            relid = RangeVarGetRelid(rv, AccessShareLock, false);

            /* Check for supported relkind. */
            CheckSubscriptionRelkind(get_rel_relkind(relid),
                                     rv->schemaname, rv->relname);

            pubrel_local_oids[off++] = relid;

            if (!bsearch(&relid, subrel_local_oids,
                         list_length(subrel_states), sizeof(Oid), oid_cmp))
            {
                AddSubscriptionRelState(sub->oid, relid,
                                        copy_data ? SUBREL_STATE_INIT : SUBREL_STATE_READY,
                                        InvalidXLogRecPtr);
                ereport(DEBUG1,
                        (errmsg_internal("table \"%s.%s\" added to subscription \"%s\"",
                                         rv->schemaname, rv->relname, sub->name)));
            }
        }

        /*
         * Next remove state for tables we should not care about anymore using
         * the data we collected above
         */
        qsort(pubrel_local_oids, list_length(pubrel_names),
              sizeof(Oid), oid_cmp);

        remove_rel_len = 0;
        for (off = 0; off < list_length(subrel_states); off++)
        {
            Oid         relid = subrel_local_oids[off];

            if (!bsearch(&relid, pubrel_local_oids,
                         list_length(pubrel_names), sizeof(Oid), oid_cmp))
            {
                char        state;
                XLogRecPtr  statelsn;

                /*
                 * Lock pg_subscription_rel with AccessExclusiveLock to
                 * prevent any race conditions with the apply worker
                 * re-launching workers at the same time this code is trying
                 * to remove those tables.
                 *
                 * Even if new worker for this particular rel is restarted it
                 * won't be able to make any progress as we hold exclusive
                 * lock on subscription_rel till the transaction end. It will
                 * simply exit as there is no corresponding rel entry.
                 *
                 * This locking also ensures that the state of rels won't
                 * change till we are done with this refresh operation.
                 */
                if (!rel)
                    rel = table_open(SubscriptionRelRelationId, AccessExclusiveLock);

                /* Last known rel state. */
                state = GetSubscriptionRelState(sub->oid, relid, &statelsn);

                sub_remove_rels[remove_rel_len].relid = relid;
                sub_remove_rels[remove_rel_len++].state = state;

                RemoveSubscriptionRel(sub->oid, relid);

                logicalrep_worker_stop(sub->oid, relid);

                /*
                 * For READY state, we would have already dropped the
                 * tablesync origin.
                 */
                if (state != SUBREL_STATE_READY)
                {
                    char        originname[NAMEDATALEN];

                    /*
                     * Drop the tablesync's origin tracking if exists.
                     *
                     * It is possible that the origin is not yet created for
                     * tablesync worker, this can happen for the states before
                     * SUBREL_STATE_FINISHEDCOPY. The apply worker can also
                     * concurrently try to drop the origin and by this time
                     * the origin might be already removed. For these reasons,
                     * passing missing_ok = true.
                     */
                    ReplicationOriginNameForTablesync(sub->oid, relid, originname,
                                                      sizeof(originname));
                    replorigin_drop_by_name(originname, true, false);
                }

                ereport(DEBUG1,
                        (errmsg_internal("table \"%s.%s\" removed from subscription \"%s\"",
                                         get_namespace_name(get_rel_namespace(relid)),
                                         get_rel_name(relid),
                                         sub->name)));
            }
        }

        /*
         * Drop the tablesync slots associated with removed tables. This has
         * to be at the end because otherwise if there is an error while doing
         * the database operations we won't be able to rollback dropped slots.
         */
        for (off = 0; off < remove_rel_len; off++)
        {
            if (sub_remove_rels[off].state != SUBREL_STATE_READY &&
                sub_remove_rels[off].state != SUBREL_STATE_SYNCDONE)
            {
                char        syncslotname[NAMEDATALEN] = {0};

                /*
                 * For READY/SYNCDONE states we know the tablesync slot has
                 * already been dropped by the tablesync worker.
                 *
                 * For other states, there is no certainty, maybe the slot
                 * does not exist yet. Also, if we fail after removing some of
                 * the slots, next time, it will again try to drop already
                 * dropped slots and fail. For these reasons, we allow
                 * missing_ok = true for the drop.
                 */
                ReplicationSlotNameForTablesync(sub->oid, sub_remove_rels[off].relid,
                                                syncslotname, sizeof(syncslotname));
                ReplicationSlotDropAtPubNode(wrconn, syncslotname, true);
            }
        }
    }
    PG_FINALLY();
    {
        walrcv_disconnect(wrconn);
    }
    PG_END_TRY();

    if (rel)
        table_close(rel, NoLock);
}

/*
 * Alter the existing subscription.
 */
ObjectAddress
AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
                  bool isTopLevel)
{
    Relation    rel;
    ObjectAddress myself;
    bool        nulls[Natts_pg_subscription];
    bool        replaces[Natts_pg_subscription];
    Datum       values[Natts_pg_subscription];
    HeapTuple   tup;
    Oid         subid;
    bool        update_tuple = false;
    Subscription *sub;
    Form_pg_subscription form;
    bits32      supported_opts;
    SubOpts     opts = {0};

    rel = table_open(SubscriptionRelationId, RowExclusiveLock);

    /* Fetch the existing tuple. */
    tup = SearchSysCacheCopy2(SUBSCRIPTIONNAME, MyDatabaseId,
                              CStringGetDatum(stmt->subname));

    if (!HeapTupleIsValid(tup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("subscription \"%s\" does not exist",
                        stmt->subname)));

    form = (Form_pg_subscription) GETSTRUCT(tup);
    subid = form->oid;

    /* must be owner */
    if (!pg_subscription_ownercheck(subid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_SUBSCRIPTION,
                       stmt->subname);

    sub = GetSubscription(subid, false);

    /* Lock the subscription so nobody else can do anything with it. */
    LockSharedObject(SubscriptionRelationId, subid, 0, AccessExclusiveLock);

    /* Form a new tuple. */
    memset(values, 0, sizeof(values));
    memset(nulls, false, sizeof(nulls));
    memset(replaces, false, sizeof(replaces));

    switch (stmt->kind)
    {
        case ALTER_SUBSCRIPTION_OPTIONS:
            {
                supported_opts = (SUBOPT_SLOT_NAME |
                                  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
                                  SUBOPT_STREAMING);

                parse_subscription_options(pstate, stmt->options,
                                           supported_opts, &opts);

                if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
                {
                    /*
                     * The subscription must be disabled to allow slot_name as
                     * 'none', otherwise, the apply worker will repeatedly try
                     * to stream the data using that slot_name which neither
                     * exists on the publisher nor the user will be allowed to
                     * create it.
                     */
                    if (sub->enabled && !opts.slot_name)
                        ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("cannot set %s for enabled subscription",
                                        "slot_name = NONE")));

                    if (opts.slot_name)
                        values[Anum_pg_subscription_subslotname - 1] =
                            DirectFunctionCall1(namein, CStringGetDatum(opts.slot_name));
                    else
                        nulls[Anum_pg_subscription_subslotname - 1] = true;
                    replaces[Anum_pg_subscription_subslotname - 1] = true;
                }

                if (opts.synchronous_commit)
                {
                    values[Anum_pg_subscription_subsynccommit - 1] =
                        CStringGetTextDatum(opts.synchronous_commit);
                    replaces[Anum_pg_subscription_subsynccommit - 1] = true;
                }

                if (IsSet(opts.specified_opts, SUBOPT_BINARY))
                {
                    values[Anum_pg_subscription_subbinary - 1] =
                        BoolGetDatum(opts.binary);
                    replaces[Anum_pg_subscription_subbinary - 1] = true;
                }

                if (IsSet(opts.specified_opts, SUBOPT_STREAMING))
                {
                    values[Anum_pg_subscription_substream - 1] =
                        BoolGetDatum(opts.streaming);
                    replaces[Anum_pg_subscription_substream - 1] = true;
                }

                update_tuple = true;
                break;
            }

        case ALTER_SUBSCRIPTION_ENABLED:
            {
                parse_subscription_options(pstate, stmt->options,
                                           SUBOPT_ENABLED, &opts);
                Assert(IsSet(opts.specified_opts, SUBOPT_ENABLED));

                if (!sub->slotname && opts.enabled)
                    ereport(ERROR,
                            (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                             errmsg("cannot enable subscription that does not have a slot name")));

                values[Anum_pg_subscription_subenabled - 1] =
                    BoolGetDatum(opts.enabled);
                replaces[Anum_pg_subscription_subenabled - 1] = true;

                if (opts.enabled)
                    ApplyLauncherWakeupAtCommit();

                update_tuple = true;
                break;
            }

        case ALTER_SUBSCRIPTION_CONNECTION:
            /* Load the library providing us libpq calls. */
            load_file("libpqwalreceiver", false);
            /* Check the connection info string. */
            walrcv_check_conninfo(stmt->conninfo);

            values[Anum_pg_subscription_subconninfo - 1] =
                CStringGetTextDatum(stmt->conninfo);
            replaces[Anum_pg_subscription_subconninfo - 1] = true;
            update_tuple = true;
            break;

        case ALTER_SUBSCRIPTION_SET_PUBLICATION:
            {
                supported_opts = SUBOPT_COPY_DATA | SUBOPT_REFRESH;
                parse_subscription_options(pstate, stmt->options,
                                           supported_opts, &opts);

                values[Anum_pg_subscription_subpublications - 1] =
                    publicationListToArray(stmt->publication);
                replaces[Anum_pg_subscription_subpublications - 1] = true;

                update_tuple = true;

                /* Refresh if user asked us to. */
                if (opts.refresh)
                {
                    if (!sub->enabled)
                        ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("ALTER SUBSCRIPTION with refresh is not allowed for disabled subscriptions"),
                                 errhint("Use ALTER SUBSCRIPTION ... SET PUBLICATION ... WITH (refresh = false).")));

                    /*
                     * See ALTER_SUBSCRIPTION_REFRESH for details why this is
                     * not allowed.
                     */
                    if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED && opts.copy_data)
                        ereport(ERROR,
                                (errcode(ERRCODE_SYNTAX_ERROR),
                                 errmsg("ALTER SUBSCRIPTION with refresh and copy_data is not allowed when two_phase is enabled"),
                                 errhint("Use ALTER SUBSCRIPTION ...SET PUBLICATION with refresh = false, or with copy_data = false"
                                         ", or use DROP/CREATE SUBSCRIPTION.")));

                    PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION with refresh");

                    /* Make sure refresh sees the new list of publications. */
                    sub->publications = stmt->publication;

                    AlterSubscription_refresh(sub, opts.copy_data);
                }

                break;
            }

        case ALTER_SUBSCRIPTION_ADD_PUBLICATION:
        case ALTER_SUBSCRIPTION_DROP_PUBLICATION:
            {
                List       *publist;
                bool        isadd = stmt->kind == ALTER_SUBSCRIPTION_ADD_PUBLICATION;

                supported_opts = SUBOPT_REFRESH | SUBOPT_COPY_DATA;
                parse_subscription_options(pstate, stmt->options,
                                           supported_opts, &opts);

                publist = merge_publications(sub->publications, stmt->publication, isadd, stmt->subname);
                values[Anum_pg_subscription_subpublications - 1] =
                    publicationListToArray(publist);
                replaces[Anum_pg_subscription_subpublications - 1] = true;

                update_tuple = true;

                /* Refresh if user asked us to. */
                if (opts.refresh)
                {
                    if (!sub->enabled)
                        ereport(ERROR,
                                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                                 errmsg("ALTER SUBSCRIPTION with refresh is not allowed for disabled subscriptions"),
                                 errhint("Use ALTER SUBSCRIPTION ... SET PUBLICATION ... WITH (refresh = false).")));

                    /*
                     * See ALTER_SUBSCRIPTION_REFRESH for details why this is
                     * not allowed.
                     */
                    if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED && opts.copy_data)
                        ereport(ERROR,
                                (errcode(ERRCODE_SYNTAX_ERROR),
                                 errmsg("ALTER SUBSCRIPTION with refresh and copy_data is not allowed when two_phase is enabled"),
                                 errhint("Use ALTER SUBSCRIPTION ...SET PUBLICATION with refresh = false, or with copy_data = false"
                                         ", or use DROP/CREATE SUBSCRIPTION.")));

                    PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION with refresh");

                    /* Refresh the new list of publications. */
                    sub->publications = publist;

                    AlterSubscription_refresh(sub, opts.copy_data);
                }

                break;
            }

        case ALTER_SUBSCRIPTION_REFRESH:
            {
                if (!sub->enabled)
                    ereport(ERROR,
                            (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                             errmsg("ALTER SUBSCRIPTION ... REFRESH is not allowed for disabled subscriptions")));

                parse_subscription_options(pstate, stmt->options,
                                           SUBOPT_COPY_DATA, &opts);

                /*
                 * The subscription option "two_phase" requires that
                 * replication has passed the initial table synchronization
                 * phase before the two_phase becomes properly enabled.
                 *
                 * But, having reached this two-phase commit "enabled" state
                 * we must not allow any subsequent table initialization to
                 * occur. So the ALTER SUBSCRIPTION ... REFRESH is disallowed
                 * when the user had requested two_phase = on mode.
                 *
                 * The exception to this restriction is when copy_data =
                 * false, because when copy_data is false the tablesync will
                 * start already in READY state and will exit directly without
                 * doing anything.
                 *
                 * For more details see comments atop worker.c.
                 */
                if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED && opts.copy_data)
                    ereport(ERROR,
                            (errcode(ERRCODE_SYNTAX_ERROR),
                             errmsg("ALTER SUBSCRIPTION ... REFRESH with copy_data is not allowed when two_phase is enabled"),
                             errhint("Use ALTER SUBSCRIPTION ... REFRESH with copy_data = false"
                                     ", or use DROP/CREATE SUBSCRIPTION.")));

                PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... REFRESH");

                AlterSubscription_refresh(sub, opts.copy_data);

                break;
            }

        default:
            elog(ERROR, "unrecognized ALTER SUBSCRIPTION kind %d",
                 stmt->kind);
    }

    /* Update the catalog if needed. */
    if (update_tuple)
    {
        tup = heap_modify_tuple(tup, RelationGetDescr(rel), values, nulls,
                                replaces);

        CatalogTupleUpdate(rel, &tup->t_self, tup);

        heap_freetuple(tup);
    }

    table_close(rel, RowExclusiveLock);

    ObjectAddressSet(myself, SubscriptionRelationId, subid);

    InvokeObjectPostAlterHook(SubscriptionRelationId, subid, 0);

    return myself;
}

/*
 * Drop a subscription
 */
void
DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
{
    Relation    rel;
    ObjectAddress myself;
    HeapTuple   tup;
    Oid         subid;
    Datum       datum;
    bool        isnull;
    char       *subname;
    char       *conninfo;
    char       *slotname;
    List       *subworkers;
    ListCell   *lc;
    char        originname[NAMEDATALEN];
    char       *err = NULL;
    WalReceiverConn *wrconn;
    Form_pg_subscription form;
    List       *rstates;

    /*
     * Lock pg_subscription with AccessExclusiveLock to ensure that the
     * launcher doesn't restart new worker during dropping the subscription
     */
    rel = table_open(SubscriptionRelationId, AccessExclusiveLock);

    tup = SearchSysCache2(SUBSCRIPTIONNAME, MyDatabaseId,
                          CStringGetDatum(stmt->subname));

    if (!HeapTupleIsValid(tup))
    {
        table_close(rel, NoLock);

        if (!stmt->missing_ok)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("subscription \"%s\" does not exist",
                            stmt->subname)));
        else
            ereport(NOTICE,
                    (errmsg("subscription \"%s\" does not exist, skipping",
                            stmt->subname)));

        return;
    }

    form = (Form_pg_subscription) GETSTRUCT(tup);
    subid = form->oid;

    /* must be owner */
    if (!pg_subscription_ownercheck(subid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_SUBSCRIPTION,
                       stmt->subname);

    /* DROP hook for the subscription being removed */
    InvokeObjectDropHook(SubscriptionRelationId, subid, 0);

    /*
     * Lock the subscription so nobody else can do anything with it (including
     * the replication workers).
     */
    LockSharedObject(SubscriptionRelationId, subid, 0, AccessExclusiveLock);

    /* Get subname */
    datum = SysCacheGetAttr(SUBSCRIPTIONOID, tup,
                            Anum_pg_subscription_subname, &isnull);
    Assert(!isnull);
    subname = pstrdup(NameStr(*DatumGetName(datum)));

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

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

    /*
     * Since dropping a replication slot is not transactional, the replication
     * slot stays dropped even if the transaction rolls back.  So we cannot
     * run DROP SUBSCRIPTION inside a transaction block if dropping the
     * replication slot.
     *
     * XXX The command name should really be something like "DROP SUBSCRIPTION
     * of a subscription that is associated with a replication slot", but we
     * don't have the proper facilities for that.
     */
    if (slotname)
        PreventInTransactionBlock(isTopLevel, "DROP SUBSCRIPTION");

    ObjectAddressSet(myself, SubscriptionRelationId, subid);
    EventTriggerSQLDropAddObject(&myself, true, true);

    /* Remove the tuple from catalog. */
    CatalogTupleDelete(rel, &tup->t_self);

    ReleaseSysCache(tup);

    /*
     * Stop all the subscription workers immediately.
     *
     * This is necessary if we are dropping the replication slot, so that the
     * slot becomes accessible.
     *
     * It is also necessary if the subscription is disabled and was disabled
     * in the same transaction.  Then the workers haven't seen the disabling
     * yet and will still be running, leading to hangs later when we want to
     * drop the replication origin.  If the subscription was disabled before
     * this transaction, then there shouldn't be any workers left, so this
     * won't make a difference.
     *
     * New workers won't be started because we hold an exclusive lock on the
     * subscription till the end of the transaction.
     */
    LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
    subworkers = logicalrep_workers_find(subid, false);
    LWLockRelease(LogicalRepWorkerLock);
    foreach(lc, subworkers)
    {
        LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);

        logicalrep_worker_stop(w->subid, w->relid);
    }
    list_free(subworkers);

    /*
     * Cleanup of tablesync replication origins.
     *
     * Any READY-state relations would already have dealt with clean-ups.
     *
     * Note that the state can't change because we have already stopped both
     * the apply and tablesync workers and they can't restart because of
     * exclusive lock on the subscription.
     */
    rstates = GetSubscriptionNotReadyRelations(subid);
    foreach(lc, rstates)
    {
        SubscriptionRelState *rstate = (SubscriptionRelState *) lfirst(lc);
        Oid         relid = rstate->relid;

        /* Only cleanup resources of tablesync workers */
        if (!OidIsValid(relid))
            continue;

        /*
         * Drop the tablesync's origin tracking if exists.
         *
         * It is possible that the origin is not yet created for tablesync
         * worker so passing missing_ok = true. This can happen for the states
         * before SUBREL_STATE_FINISHEDCOPY.
         */
        ReplicationOriginNameForTablesync(subid, relid, originname,
                                          sizeof(originname));
        replorigin_drop_by_name(originname, true, false);
    }

    /* Clean up dependencies */
    deleteSharedDependencyRecordsFor(SubscriptionRelationId, subid, 0);

    /* Remove any associated relation synchronization states. */
    RemoveSubscriptionRel(subid, InvalidOid);

    /* Remove the origin tracking if exists. */
    snprintf(originname, sizeof(originname), "pg_%u", subid);
    replorigin_drop_by_name(originname, true, false);

    /*
     * If there is no slot associated with the subscription, we can finish
     * here.
     */
    if (!slotname && rstates == NIL)
    {
        table_close(rel, NoLock);
        return;
    }

    /*
     * Try to acquire the connection necessary for dropping slots.
     *
     * Note: If the slotname is NONE/NULL then we allow the command to finish
     * and users need to manually cleanup the apply and tablesync worker slots
     * later.
     *
     * This has to be at the end because otherwise if there is an error while
     * doing the database operations we won't be able to rollback dropped
     * slot.
     */
    load_file("libpqwalreceiver", false);

    wrconn = walrcv_connect(conninfo, true, subname, &err);
    if (wrconn == NULL)
    {
        if (!slotname)
        {
            /* be tidy */
            list_free(rstates);
            table_close(rel, NoLock);
            return;
        }
        else
        {
            ReportSlotConnectionError(rstates, subid, slotname, err);
        }
    }

    PG_TRY();
    {
        foreach(lc, rstates)
        {
            SubscriptionRelState *rstate = (SubscriptionRelState *) lfirst(lc);
            Oid         relid = rstate->relid;

            /* Only cleanup resources of tablesync workers */
            if (!OidIsValid(relid))
                continue;

            /*
             * Drop the tablesync slots associated with removed tables.
             *
             * For SYNCDONE/READY states, the tablesync slot is known to have
             * already been dropped by the tablesync worker.
             *
             * For other states, there is no certainty, maybe the slot does
             * not exist yet. Also, if we fail after removing some of the
             * slots, next time, it will again try to drop already dropped
             * slots and fail. For these reasons, we allow missing_ok = true
             * for the drop.
             */
            if (rstate->state != SUBREL_STATE_SYNCDONE)
            {
                char        syncslotname[NAMEDATALEN] = {0};

                ReplicationSlotNameForTablesync(subid, relid, syncslotname,
                                                sizeof(syncslotname));
                ReplicationSlotDropAtPubNode(wrconn, syncslotname, true);
            }
        }

        list_free(rstates);

        /*
         * If there is a slot associated with the subscription, then drop the
         * replication slot at the publisher.
         */
        if (slotname)
            ReplicationSlotDropAtPubNode(wrconn, slotname, false);

    }
    PG_FINALLY();
    {
        walrcv_disconnect(wrconn);
    }
    PG_END_TRY();

    table_close(rel, NoLock);
}

/*
 * Drop the replication slot at the publisher node using the replication
 * connection.
 *
 * missing_ok - if true then only issue a LOG message if the slot doesn't
 * exist.
 */
void
ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname, bool missing_ok)
{
    StringInfoData cmd;

    Assert(wrconn);

    load_file("libpqwalreceiver", false);

    initStringInfo(&cmd);
    appendStringInfo(&cmd, "DROP_REPLICATION_SLOT %s WAIT", quote_identifier(slotname));

    PG_TRY();
    {
        WalRcvExecResult *res;

        res = walrcv_exec(wrconn, cmd.data, 0, NULL);

        if (res->status == WALRCV_OK_COMMAND)
        {
            /* NOTICE. Success. */
            ereport(NOTICE,
                    (errmsg("dropped replication slot \"%s\" on publisher",
                            slotname)));
        }
        else if (res->status == WALRCV_ERROR &&
                 missing_ok &&
                 res->sqlstate == ERRCODE_UNDEFINED_OBJECT)
        {
            /* LOG. Error, but missing_ok = true. */
            ereport(LOG,
                    (errmsg("could not drop replication slot \"%s\" on publisher: %s",
                            slotname, res->err)));
        }
        else
        {
            /* ERROR. */
            ereport(ERROR,
                    (errcode(ERRCODE_CONNECTION_FAILURE),
                     errmsg("could not drop replication slot \"%s\" on publisher: %s",
                            slotname, res->err)));
        }

        walrcv_clear_result(res);
    }
    PG_FINALLY();
    {
        pfree(cmd.data);
    }
    PG_END_TRY();
}

/*
 * Internal workhorse for changing a subscription owner
 */
static void
AlterSubscriptionOwner_internal(Relation rel, HeapTuple tup, Oid newOwnerId)
{
    Form_pg_subscription form;

    form = (Form_pg_subscription) GETSTRUCT(tup);

    if (form->subowner == newOwnerId)
        return;

    if (!pg_subscription_ownercheck(form->oid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_SUBSCRIPTION,
                       NameStr(form->subname));

    /* New owner must be a superuser */
    if (!superuser_arg(newOwnerId))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied to change owner of subscription \"%s\"",
                        NameStr(form->subname)),
                 errhint("The owner of a subscription must be a superuser.")));

    form->subowner = newOwnerId;
    CatalogTupleUpdate(rel, &tup->t_self, tup);

    /* Update owner dependency reference */
    changeDependencyOnOwner(SubscriptionRelationId,
                            form->oid,
                            newOwnerId);

    InvokeObjectPostAlterHook(SubscriptionRelationId,
                              form->oid, 0);
}

/*
 * Change subscription owner -- by name
 */
ObjectAddress
AlterSubscriptionOwner(const char *name, Oid newOwnerId)
{
    Oid         subid;
    HeapTuple   tup;
    Relation    rel;
    ObjectAddress address;
    Form_pg_subscription form;

    rel = table_open(SubscriptionRelationId, RowExclusiveLock);

    tup = SearchSysCacheCopy2(SUBSCRIPTIONNAME, MyDatabaseId,
                              CStringGetDatum(name));

    if (!HeapTupleIsValid(tup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("subscription \"%s\" does not exist", name)));

    form = (Form_pg_subscription) GETSTRUCT(tup);
    subid = form->oid;

    AlterSubscriptionOwner_internal(rel, tup, newOwnerId);

    ObjectAddressSet(address, SubscriptionRelationId, subid);

    heap_freetuple(tup);

    table_close(rel, RowExclusiveLock);

    return address;
}

/*
 * Change subscription owner -- by OID
 */
void
AlterSubscriptionOwner_oid(Oid subid, Oid newOwnerId)
{
    HeapTuple   tup;
    Relation    rel;

    rel = table_open(SubscriptionRelationId, RowExclusiveLock);

    tup = SearchSysCacheCopy1(SUBSCRIPTIONOID, ObjectIdGetDatum(subid));

    if (!HeapTupleIsValid(tup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("subscription with OID %u does not exist", subid)));

    AlterSubscriptionOwner_internal(rel, tup, newOwnerId);

    heap_freetuple(tup);

    table_close(rel, RowExclusiveLock);
}

/*
 * Get the list of tables which belong to specified publications on the
 * publisher connection.
 */
static List *
fetch_table_list(WalReceiverConn *wrconn, List *publications)
{
    WalRcvExecResult *res;
    StringInfoData cmd;
    TupleTableSlot *slot;
    Oid         tableRow[2] = {TEXTOID, TEXTOID};
    ListCell   *lc;
    bool        first;
    List       *tablelist = NIL;

    Assert(list_length(publications) > 0);

    initStringInfo(&cmd);
    appendStringInfoString(&cmd, "SELECT DISTINCT t.schemaname, t.tablename\n"
                           "  FROM pg_catalog.pg_publication_tables t\n"
                           " WHERE t.pubname IN (");
    first = true;
    foreach(lc, publications)
    {
        char       *pubname = strVal(lfirst(lc));

        if (first)
            first = false;
        else
            appendStringInfoString(&cmd, ", ");

        appendStringInfoString(&cmd, quote_literal_cstr(pubname));
    }
    appendStringInfoChar(&cmd, ')');

    res = walrcv_exec(wrconn, cmd.data, 2, tableRow);
    pfree(cmd.data);

    if (res->status != WALRCV_OK_TUPLES)
        ereport(ERROR,
                (errcode(ERRCODE_CONNECTION_FAILURE),
                 errmsg("could not receive list of replicated tables from the publisher: %s",
                        res->err)));

    /* Process tables. */
    slot = MakeSingleTupleTableSlot(res->tupledesc, &TTSOpsMinimalTuple);
    while (tuplestore_gettupleslot(res->tuplestore, true, false, slot))
    {
        char       *nspname;
        char       *relname;
        bool        isnull;
        RangeVar   *rv;

        nspname = TextDatumGetCString(slot_getattr(slot, 1, &isnull));
        Assert(!isnull);
        relname = TextDatumGetCString(slot_getattr(slot, 2, &isnull));
        Assert(!isnull);

        rv = makeRangeVar(nspname, relname, -1);
        tablelist = lappend(tablelist, rv);

        ExecClearTuple(slot);
    }
    ExecDropSingleTupleTableSlot(slot);

    walrcv_clear_result(res);

    return tablelist;
}

/*
 * This is to report the connection failure while dropping replication slots.
 * Here, we report the WARNING for all tablesync slots so that user can drop
 * them manually, if required.
 */
static void
ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err)
{
    ListCell   *lc;

    foreach(lc, rstates)
    {
        SubscriptionRelState *rstate = (SubscriptionRelState *) lfirst(lc);
        Oid         relid = rstate->relid;

        /* Only cleanup resources of tablesync workers */
        if (!OidIsValid(relid))
            continue;

        /*
         * Caller needs to ensure that relstate doesn't change underneath us.
         * See DropSubscription where we get the relstates.
         */
        if (rstate->state != SUBREL_STATE_SYNCDONE)
        {
            char        syncslotname[NAMEDATALEN] = {0};

            ReplicationSlotNameForTablesync(subid, relid, syncslotname,
                                            sizeof(syncslotname));
            elog(WARNING, "could not drop tablesync replication slot \"%s\"",
                 syncslotname);
        }
    }

    ereport(ERROR,
            (errcode(ERRCODE_CONNECTION_FAILURE),
             errmsg("could not connect to publisher when attempting to "
                    "drop replication slot \"%s\": %s", slotname, err),
    /* translator: %s is an SQL ALTER command */
             errhint("Use %s to disassociate the subscription from the slot.",
                     "ALTER SUBSCRIPTION ... SET (slot_name = NONE)")));
}

/*
 * Check for duplicates in the given list of publications and error out if
 * found one.  Add publications to datums as text datums, if datums is not
 * NULL.
 */
static void
check_duplicates_in_publist(List *publist, Datum *datums)
{
    ListCell   *cell;
    int         j = 0;

    foreach(cell, publist)
    {
        char       *name = strVal(lfirst(cell));
        ListCell   *pcell;

        foreach(pcell, publist)
        {
            char       *pname = strVal(lfirst(pcell));

            if (pcell == cell)
                break;

            if (strcmp(name, pname) == 0)
                ereport(ERROR,
                        (errcode(ERRCODE_DUPLICATE_OBJECT),
                         errmsg("publication name \"%s\" used more than once",
                                pname)));
        }

        if (datums)
            datums[j++] = CStringGetTextDatum(name);
    }
}

/*
 * Merge current subscription's publications and user-specified publications
 * from ADD/DROP PUBLICATIONS.
 *
 * If addpub is true, we will add the list of publications into oldpublist.
 * Otherwise, we will delete the list of publications from oldpublist.  The
 * returned list is a copy, oldpublist itself is not changed.
 *
 * subname is the subscription name, for error messages.
 */
static List *
merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname)
{
    ListCell   *lc;

    oldpublist = list_copy(oldpublist);

    check_duplicates_in_publist(newpublist, NULL);

    foreach(lc, newpublist)
    {
        char       *name = strVal(lfirst(lc));
        ListCell   *lc2;
        bool        found = false;

        foreach(lc2, oldpublist)
        {
            char       *pubname = strVal(lfirst(lc2));

            if (strcmp(name, pubname) == 0)
            {
                found = true;
                if (addpub)
                    ereport(ERROR,
                            (errcode(ERRCODE_DUPLICATE_OBJECT),
                             errmsg("publication \"%s\" is already in subscription \"%s\"",
                                    name, subname)));
                else
                    oldpublist = foreach_delete_current(oldpublist, lc2);

                break;
            }
        }

        if (addpub && !found)
            oldpublist = lappend(oldpublist, makeString(name));
        else if (!addpub && !found)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("publication \"%s\" is not in subscription \"%s\"",
                            name, subname)));
    }

    /*
     * XXX Probably no strong reason for this, but for now it's to make ALTER
     * SUBSCRIPTION ... DROP PUBLICATION consistent with SET PUBLICATION.
     */
    if (!oldpublist)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("cannot drop all the publications from a subscription")));

    return oldpublist;
}