postgres/src/backend/commands/subscriptioncmds.c

/*-------------------------------------------------------------------------
 *
 * subscriptioncmds.c
 *		subscription catalog manipulation functions
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *		subscriptioncmds.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "miscadmin.h"

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

#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/objectaddress.h"
#include "catalog/pg_type.h"
#include "catalog/pg_subscription.h"
#include "catalog/pg_subscription_rel.h"

#include "commands/defrem.h"
#include "commands/event_trigger.h"
#include "commands/subscriptioncmds.h"

#include "nodes/makefuncs.h"

#include "replication/logicallauncher.h"
#include "replication/origin.h"
#include "replication/walreceiver.h"
#include "replication/walsender.h"
#include "replication/worker_internal.h"

#include "storage/lmgr.h"

#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"

static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);

/*
 * 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 on options if the target output pointer is NULL to
 * accomodate that.
 */
static void
parse_subscription_options(List *options, bool *connect, bool *enabled_given,
						   bool *enabled, bool *create_slot, char **slot_name,
						   bool *copy_data)
{
	ListCell   *lc;
	bool		connect_given = false;
	bool		create_slot_given = false;
	bool		copy_data_given = false;

	if (connect)
		*connect = true;
	if (enabled)
	{
		*enabled_given = false;
		*enabled = true;
	}
	if (create_slot)
		*create_slot = true;
	if (slot_name)
		*slot_name = NULL;
	if (copy_data)
		*copy_data = true;

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

		if (strcmp(defel->defname, "noconnect") == 0 && connect)
		{
			if (connect_given)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			connect_given = true;
			*connect = !defGetBoolean(defel);
		}
		else if (strcmp(defel->defname, "enabled") == 0 && enabled)
		{
			if (*enabled_given)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			*enabled_given = true;
			*enabled = defGetBoolean(defel);
		}
		else if (strcmp(defel->defname, "disabled") == 0 && enabled)
		{
			if (*enabled_given)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			*enabled_given = true;
			*enabled = !defGetBoolean(defel);
		}
		else if (strcmp(defel->defname, "create slot") == 0 && create_slot)
		{
			if (create_slot_given)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			create_slot_given = true;
			*create_slot = defGetBoolean(defel);
		}
		else if (strcmp(defel->defname, "nocreate slot") == 0 && create_slot)
		{
			if (create_slot_given)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			create_slot_given = true;
			*create_slot = !defGetBoolean(defel);
		}
		else if (strcmp(defel->defname, "slot name") == 0 && slot_name)
		{
			if (*slot_name)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			*slot_name = defGetString(defel);
		}
		else if (strcmp(defel->defname, "copy data") == 0 && copy_data)
		{
			if (copy_data_given)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			copy_data_given = true;
			*copy_data = defGetBoolean(defel);
		}
		else if (strcmp(defel->defname, "nocopy data") == 0 && copy_data)
		{
			if (copy_data_given)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("conflicting or redundant options")));

			copy_data_given = true;
			*copy_data = !defGetBoolean(defel);
		}
		else
			elog(ERROR, "unrecognized option: %s", defel->defname);
	}

	/*
	 * We've been explicitly asked to not connect, that requires some
	 * additional processing.
	 */
	if (connect && !*connect)
	{
		/* Check for incompatible options from the user. */
		if (*enabled_given && *enabled)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("noconnect and enabled are mutually exclusive options")));

		if (create_slot_given && *create_slot)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("noconnect and create slot are mutually exclusive options")));

		if (copy_data_given && *copy_data)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("noconnect and copy data are mutually exclusive options")));

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

/*
 * Auxiliary function to return a text array out of a list of String nodes.
 */
static Datum
publicationListToArray(List *publist)
{
	ArrayType  *arr;
	Datum	   *datums;
	int			j = 0;
	ListCell   *cell;
	MemoryContext memcxt;
	MemoryContext oldcxt;

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

	datums = palloc(sizeof(text *) * list_length(publist));
	foreach(cell, publist)
	{
		char	   *name = strVal(lfirst(cell));
		ListCell   *pcell;

		/* Check for duplicates. */
		foreach(pcell, publist)
		{
			char	   *pname = strVal(lfirst(cell));

			if (name == pname)
				break;

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

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

	MemoryContextSwitchTo(oldcxt);

	arr = construct_array(datums, list_length(publist),
						  TEXTOID, -1, false, 'i');
	MemoryContextDelete(memcxt);

	return PointerGetDatum(arr);
}

/*
 * Create new subscription.
 */
ObjectAddress
CreateSubscription(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;
	bool		connect;
	bool		enabled_given;
	bool		enabled;
	bool		copy_data;
	char	   *conninfo;
	char	   *slotname;
	char		originname[NAMEDATALEN];
	bool		create_slot;
	List	   *publications;

	/*
	 * Parse and check options.
	 * Connection and publication should not be specified here.
	 */
	parse_subscription_options(stmt->options, &connect, &enabled_given,
							   &enabled, &create_slot, &slotname, &copy_data);

	/*
	 * 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 (create_slot)
		PreventTransactionChain(isTopLevel, "CREATE SUBSCRIPTION ... CREATE SLOT");

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

	rel = heap_open(SubscriptionRelationId, RowExclusiveLock);

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

	if (slotname == NULL)
		slotname = stmt->subname;

	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));

	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(enabled);
	values[Anum_pg_subscription_subconninfo - 1] =
		CStringGetTextDatum(conninfo);
	values[Anum_pg_subscription_subslotname - 1] =
		DirectFunctionCall1(namein, CStringGetDatum(slotname));
	values[Anum_pg_subscription_subpublications - 1] =
		 publicationListToArray(publications);

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

	/* Insert tuple into catalog. */
	subid = 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 (connect)
	{
		XLogRecPtr			lsn;
		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,
					(errmsg("could not connect to the publisher: %s", err)));

		PG_TRY();
		{
			/*
			 * If requested, create permanent slot for the subscription.
			 * We won't use the initial snapshot for anything, so no need
			 * to export it.
			 */
			if (create_slot)
			{
				walrcv_create_slot(wrconn, slotname, false,
								   CRS_NOEXPORT_SNAPSHOT, &lsn);
				ereport(NOTICE,
						(errmsg("created replication slot \"%s\" on publisher",
								slotname)));
			}

			/*
			 * Set sync state based on if we were asked to do data copy or
			 * not.
			 */
			table_state = 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);

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

			ereport(NOTICE,
					(errmsg("synchronized table states")));
		}
		PG_CATCH();
		{
			/* Close the connection in case of failure. */
			walrcv_disconnect(wrconn);
			PG_RE_THROW();
		}
		PG_END_TRY();

		/* And we are done with the remote side. */
		walrcv_disconnect(wrconn);
	}
	else
		ereport(WARNING,
				(errmsg("tables were not subscribed, you will have to run "
						"ALTER SUBSCRIPTION ... REFRESH PUBLICATION to "
						"subscribe the tables")));

	heap_close(rel, RowExclusiveLock);

	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;

	/* 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,
				(errmsg("could not connect to the publisher: %s", err)));

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

	/* We are done with the remote side, close connection. */
	walrcv_disconnect(wrconn);

	/* 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);

	/*
	 * 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);
		pubrel_local_oids[off++] = relid;

		if (!bsearch(&relid, subrel_local_oids,
					 list_length(subrel_states), sizeof(Oid), oid_cmp))
		{
			SetSubscriptionRelState(sub->oid, relid,
									copy_data ? SUBREL_STATE_INIT : SUBREL_STATE_READY,
									InvalidXLogRecPtr);
			ereport(NOTICE,
					(errmsg("added subscription for table %s.%s",
							quote_identifier(rv->schemaname),
							quote_identifier(rv->relname))));
		}
	}

	/*
	 * 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);

	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   *namespace;

			RemoveSubscriptionRel(sub->oid, relid);

			namespace = get_namespace_name(get_rel_namespace(relid));
			ereport(NOTICE,
					(errmsg("removed subscription for table %s.%s",
							quote_identifier(namespace),
							quote_identifier(get_rel_name(relid)))));
		}
	}
}

/*
 * Alter the existing subscription.
 */
ObjectAddress
AlterSubscription(AlterSubscriptionStmt *stmt)
{
	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;

	rel = heap_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)));

	/* must be owner */
	if (!pg_subscription_ownercheck(HeapTupleGetOid(tup), GetUserId()))
		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_SUBSCRIPTION,
					   stmt->subname);

	subid = HeapTupleGetOid(tup);

	/* 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:
			{
				char *slot_name;

				parse_subscription_options(stmt->options, NULL, NULL, NULL,
										   NULL, &slot_name, NULL);

				values[Anum_pg_subscription_subslotname - 1] =
					DirectFunctionCall1(namein, CStringGetDatum(slot_name));
				replaces[Anum_pg_subscription_subslotname - 1] = true;

				update_tuple = true;
				break;
			}

		case ALTER_SUBSCRIPTION_ENABLED:
			{
				bool enabled,
					 enabled_given;

				parse_subscription_options(stmt->options, NULL,
										   &enabled_given, &enabled, NULL,
										   NULL, NULL);
				Assert(enabled_given);

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

				update_tuple = true;
				break;
			}

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

		case ALTER_SUBSCRIPTION_PUBLICATION:
		case ALTER_SUBSCRIPTION_PUBLICATION_REFRESH:
			{
				bool			copy_data;
				Subscription   *sub = GetSubscription(subid, false);

				parse_subscription_options(stmt->options, NULL, NULL, NULL,
										   NULL, NULL, &copy_data);

				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 (stmt->kind == ALTER_SUBSCRIPTION_PUBLICATION_REFRESH)
				{
					/* Make sure refresh sees the new list of publications. */
					sub->publications = stmt->publication;

					AlterSubscription_refresh(sub, copy_data);
				}

				break;
			}

		case ALTER_SUBSCRIPTION_REFRESH:
			{
				bool			copy_data;
				Subscription   *sub = GetSubscription(subid, false);

				parse_subscription_options(stmt->options, NULL, NULL, NULL,
										   NULL, NULL, &copy_data);

				AlterSubscription_refresh(sub, 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);
	}

	heap_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;
	char		originname[NAMEDATALEN];
	char	   *err = NULL;
	RepOriginId	originid;
	WalReceiverConn	   *wrconn = NULL;
	StringInfoData		cmd;

	/*
	 * 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.
	 */
	if (stmt->drop_slot)
		PreventTransactionChain(isTopLevel, "DROP SUBSCRIPTION ... DROP SLOT");

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

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

	if (!HeapTupleIsValid(tup))
	{
		heap_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;
	}

	subid = HeapTupleGetOid(tup);

	/* must be owner */
	if (!pg_subscription_ownercheck(subid, GetUserId()))
		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_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 = pstrdup(TextDatumGetCString(datum));

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

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

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

	ReleaseSysCache(tup);

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

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

	/* Kill the apply worker so that the slot becomes accessible. */
	logicalrep_worker_stop(subid, InvalidOid);

	/* Remove the origin tracking if exists. */
	snprintf(originname, sizeof(originname), "pg_%u", subid);
	originid = replorigin_by_name(originname, true);
	if (originid != InvalidRepOriginId)
		replorigin_drop(originid);

	/* If the user asked to not drop the slot, we are done mow.*/
	if (!stmt->drop_slot)
	{
		heap_close(rel, NoLock);
		return;
	}

	/*
	 * Otherwise drop the replication slot at the publisher node using
	 * the replication connection.
	 */
	load_file("libpqwalreceiver", false);

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

	wrconn = walrcv_connect(conninfo, true, subname, &err);
	if (wrconn == NULL)
		ereport(ERROR,
				(errmsg("could not connect to publisher when attempting to "
						"drop the replication slot \"%s\"", slotname),
				 errdetail("The error was: %s", err)));

	PG_TRY();
	{
		WalRcvExecResult   *res;
		res = walrcv_exec(wrconn, cmd.data, 0, NULL);

		if (res->status != WALRCV_OK_COMMAND)
			ereport(ERROR,
					(errmsg("could not drop the replication slot \"%s\" on publisher",
							slotname),
					 errdetail("The error was: %s", res->err)));
		else
			ereport(NOTICE,
					(errmsg("dropped replication slot \"%s\" on publisher",
							slotname)));

		walrcv_clear_result(res);
	}
	PG_CATCH();
	{
		/* Close the connection in case of failure */
		walrcv_disconnect(wrconn);
		PG_RE_THROW();
	}
	PG_END_TRY();

	walrcv_disconnect(wrconn);

	pfree(cmd.data);

	heap_close(rel, NoLock);
}

/*
 * 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(HeapTupleGetOid(tup), GetUserId()))
		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_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 an subscription must be a superuser.")));

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

	/* Update owner dependency reference */
	changeDependencyOnOwner(SubscriptionRelationId,
							HeapTupleGetOid(tup),
							newOwnerId);

	InvokeObjectPostAlterHook(SubscriptionRelationId,
							  HeapTupleGetOid(tup), 0);
}

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

	rel = heap_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)));

	subid = HeapTupleGetOid(tup);

	AlterSubscriptionOwner_internal(rel, tup, newOwnerId);

	ObjectAddressSet(address, SubscriptionRelationId, subid);

	heap_freetuple(tup);

	heap_close(rel, RowExclusiveLock);

	return address;
}

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

	rel = heap_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);

	heap_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);
	appendStringInfo(&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, ", ");

		appendStringInfo(&cmd, "%s", quote_literal_cstr(pubname));
	}
	appendStringInfoString(&cmd, ")");

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

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

	/* Process tables. */
	slot = MakeSingleTupleTableSlot(res->tupledesc);
	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(pstrdup(nspname), pstrdup(relname), -1);
		tablelist = lappend(tablelist, rv);

		ExecClearTuple(slot);
	}
	ExecDropSingleTupleTableSlot(slot);

	walrcv_clear_result(res);

	return tablelist;
}