Logical replication

- Add PUBLICATION catalogs and DDL
- Add SUBSCRIPTION catalog and DDL
- Define logical replication protocol and output plugin
- Add logical replication workers

From: Petr Jelinek <petr@2ndquadrant.com>
Reviewed-by: Steve Singer <steve@ssinger.info>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Erik Rijkers <er@xs4all.nl>
Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

src/backend/replication/pgoutput/pgoutput.c

@@ -0,0 +1,596 @@
+/*-------------------------------------------------------------------------
+ *
+ * pgoutput.c
+ *		Logical Replication output plugin
+ *
+ * Copyright (c) 2012-2015, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		  src/backend/replication/pgoutput/pgoutput.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "catalog/pg_publication.h"
+
+#include "replication/logical.h"
+#include "replication/logicalproto.h"
+#include "replication/origin.h"
+#include "replication/pgoutput.h"
+
+#include "utils/builtins.h"
+#include "utils/inval.h"
+#include "utils/int8.h"
+#include "utils/memutils.h"
+#include "utils/syscache.h"
+
+PG_MODULE_MAGIC;
+
+extern void _PG_output_plugin_init(OutputPluginCallbacks *cb);
+
+static void pgoutput_startup(LogicalDecodingContext * ctx,
+							  OutputPluginOptions *opt, bool is_init);
+static void pgoutput_shutdown(LogicalDecodingContext * ctx);
+static void pgoutput_begin_txn(LogicalDecodingContext *ctx,
+					ReorderBufferTXN *txn);
+static void pgoutput_commit_txn(LogicalDecodingContext *ctx,
+					 ReorderBufferTXN *txn, XLogRecPtr commit_lsn);
+static void pgoutput_change(LogicalDecodingContext *ctx,
+				 ReorderBufferTXN *txn, Relation rel,
+				 ReorderBufferChange *change);
+static bool pgoutput_origin_filter(LogicalDecodingContext *ctx,
+						RepOriginId origin_id);
+
+static bool publications_valid;
+
+static List *LoadPublications(List *pubnames);
+static void publication_invalidation_cb(Datum arg, int cacheid,
+										uint32 hashvalue);
+
+/* Entry in the map used to remember which relation schemas we sent. */
+typedef struct RelationSyncEntry
+{
+	Oid		relid;			/* relation oid */
+	bool	schema_sent;	/* did we send the schema? */
+	bool	replicate_valid;
+	PublicationActions pubactions;
+} RelationSyncEntry;
+
+/* Map used to remember which relation schemas we sent. */
+static HTAB *RelationSyncCache = NULL;
+
+static void init_rel_sync_cache(MemoryContext decoding_context);
+static RelationSyncEntry *get_rel_sync_entry(PGOutputData *data, Oid relid);
+static void rel_sync_cache_relation_cb(Datum arg, Oid relid);
+static void rel_sync_cache_publication_cb(Datum arg, int cacheid,
+										  uint32 hashvalue);
+
+/*
+ * Specify output plugin callbacks
+ */
+void
+_PG_output_plugin_init(OutputPluginCallbacks *cb)
+{
+	AssertVariableIsOfType(&_PG_output_plugin_init, LogicalOutputPluginInit);
+
+	cb->startup_cb = pgoutput_startup;
+	cb->begin_cb = pgoutput_begin_txn;
+	cb->change_cb = pgoutput_change;
+	cb->commit_cb = pgoutput_commit_txn;
+	cb->filter_by_origin_cb = pgoutput_origin_filter;
+	cb->shutdown_cb = pgoutput_shutdown;
+}
+
+static void
+parse_output_parameters(List *options, uint32 *protocol_version,
+						List **publication_names)
+{
+	ListCell   *lc;
+	bool		protocol_version_given = false;
+	bool		publication_names_given = false;
+
+	foreach(lc, options)
+	{
+		DefElem    *defel = (DefElem *) lfirst(lc);
+
+		Assert(defel->arg == NULL || IsA(defel->arg, String));
+
+		/* Check each param, whether or not we recognise it */
+		if (strcmp(defel->defname, "proto_version") == 0)
+		{
+			int64		parsed;
+
+			if (protocol_version_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			protocol_version_given = true;
+
+			if (!scanint8(strVal(defel->arg), true, &parsed))
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("invalid proto_version")));
+
+			if (parsed > PG_UINT32_MAX || parsed < 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("proto_verson \"%s\" out of range",
+								strVal(defel->arg))));
+
+			*protocol_version = (uint32) parsed;
+		}
+		else if (strcmp(defel->defname, "publication_names") == 0)
+		{
+			if (publication_names_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			publication_names_given = true;
+
+			if (!SplitIdentifierString(strVal(defel->arg), ',',
+									   publication_names))
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_NAME),
+							 errmsg("invalid publication_names syntax")));
+		}
+		else
+			elog(ERROR, "unrecognized pgoutput option: %s", defel->defname);
+	}
+}
+
+/*
+ * Initialize this plugin
+ */
+static void
+pgoutput_startup(LogicalDecodingContext * ctx, OutputPluginOptions *opt,
+				  bool is_init)
+{
+	PGOutputData   *data = palloc0(sizeof(PGOutputData));
+
+	/* Create our memory context for private allocations. */
+	data->context = AllocSetContextCreate(ctx->context,
+										  "logical replication output context",
+										  ALLOCSET_DEFAULT_MINSIZE,
+										  ALLOCSET_DEFAULT_INITSIZE,
+										  ALLOCSET_DEFAULT_MAXSIZE);
+
+	ctx->output_plugin_private = data;
+
+	/* This plugin uses binary protocol. */
+	opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+
+	/*
+	 * This is replication start and not slot initialization.
+	 *
+	 * Parse and validate options passed by the client.
+	 */
+	if (!is_init)
+	{
+		/* Parse the params and ERROR if we see any we don't recognise */
+		parse_output_parameters(ctx->output_plugin_options,
+								&data->protocol_version,
+								&data->publication_names);
+
+		/* Check if we support requested protol */
+		if (data->protocol_version != LOGICALREP_PROTO_VERSION_NUM)
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("client sent proto_version=%d but we only support protocol %d or lower",
+					 data->protocol_version, LOGICALREP_PROTO_VERSION_NUM)));
+
+		if (data->protocol_version < LOGICALREP_PROTO_MIN_VERSION_NUM)
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("client sent proto_version=%d but we only support protocol %d or higher",
+				   data->protocol_version, LOGICALREP_PROTO_MIN_VERSION_NUM)));
+
+		if (list_length(data->publication_names) < 1)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("publication_names parameter missing")));
+
+		/* Init publication state. */
+		data->publications = NIL;
+		publications_valid = false;
+		CacheRegisterSyscacheCallback(PUBLICATIONOID,
+									  publication_invalidation_cb,
+									  (Datum) 0);
+
+		/* Initialize relation schema cache. */
+		init_rel_sync_cache(CacheMemoryContext);
+	}
+}
+
+/*
+ * BEGIN callback
+ */
+static void
+pgoutput_begin_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn)
+{
+	bool	send_replication_origin = txn->origin_id != InvalidRepOriginId;
+
+	OutputPluginPrepareWrite(ctx, !send_replication_origin);
+	logicalrep_write_begin(ctx->out, txn);
+
+	if (send_replication_origin)
+	{
+		char *origin;
+
+		/* Message boundary */
+		OutputPluginWrite(ctx, false);
+		OutputPluginPrepareWrite(ctx, true);
+
+		/*
+		 * XXX: which behaviour we want here?
+		 *
+		 * Alternatives:
+		 *  - don't send origin message if origin name not found
+		 *    (that's what we do now)
+		 *  - throw error - that will break replication, not good
+		 *  - send some special "unknown" origin
+		 */
+		if (replorigin_by_oid(txn->origin_id, true, &origin))
+			logicalrep_write_origin(ctx->out, origin, txn->origin_lsn);
+	}
+
+	OutputPluginWrite(ctx, true);
+}
+
+/*
+ * COMMIT callback
+ */
+static void
+pgoutput_commit_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
+					 XLogRecPtr commit_lsn)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	logicalrep_write_commit(ctx->out, txn, commit_lsn);
+	OutputPluginWrite(ctx, true);
+}
+
+/*
+ * Sends the decoded DML over wire.
+ */
+static void
+pgoutput_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
+				Relation relation, ReorderBufferChange *change)
+{
+	PGOutputData	   *data = (PGOutputData *) ctx->output_plugin_private;
+	MemoryContext		old;
+	RelationSyncEntry  *relentry;
+
+	relentry = get_rel_sync_entry(data, RelationGetRelid(relation));
+
+	/* First check the table filter */
+	switch (change->action)
+	{
+		case REORDER_BUFFER_CHANGE_INSERT:
+			if (!relentry->pubactions.pubinsert)
+				return;
+			break;
+		case REORDER_BUFFER_CHANGE_UPDATE:
+			if (!relentry->pubactions.pubupdate)
+				return;
+			break;
+		case REORDER_BUFFER_CHANGE_DELETE:
+			if (!relentry->pubactions.pubdelete)
+				return;
+			break;
+		default:
+			Assert(false);
+	}
+
+	/* Avoid leaking memory by using and resetting our own context */
+	old = MemoryContextSwitchTo(data->context);
+
+	/*
+	 * Write the relation schema if the current schema haven't been sent yet.
+	 */
+	if (!relentry->schema_sent)
+	{
+		TupleDesc	desc;
+		int			i;
+
+		desc = RelationGetDescr(relation);
+
+		/*
+		 * Write out type info if needed. We do that only for user created
+		 * types.
+		 */
+		for (i = 0; i < desc->natts; i++)
+		{
+			Form_pg_attribute att = desc->attrs[i];
+
+			if (att->attisdropped)
+				continue;
+
+			if (att->atttypid < FirstNormalObjectId)
+				continue;
+
+			OutputPluginPrepareWrite(ctx, false);
+			logicalrep_write_typ(ctx->out, att->atttypid);
+			OutputPluginWrite(ctx, false);
+		}
+
+		OutputPluginPrepareWrite(ctx, false);
+		logicalrep_write_rel(ctx->out, relation);
+		OutputPluginWrite(ctx, false);
+		relentry->schema_sent = true;
+	}
+
+	/* Send the data */
+	switch (change->action)
+	{
+		case REORDER_BUFFER_CHANGE_INSERT:
+			OutputPluginPrepareWrite(ctx, true);
+			logicalrep_write_insert(ctx->out, relation,
+									&change->data.tp.newtuple->tuple);
+			OutputPluginWrite(ctx, true);
+			break;
+		case REORDER_BUFFER_CHANGE_UPDATE:
+			{
+				HeapTuple oldtuple = change->data.tp.oldtuple ?
+					&change->data.tp.oldtuple->tuple : NULL;
+
+				OutputPluginPrepareWrite(ctx, true);
+				logicalrep_write_update(ctx->out, relation, oldtuple,
+										&change->data.tp.newtuple->tuple);
+				OutputPluginWrite(ctx, true);
+				break;
+			}
+		case REORDER_BUFFER_CHANGE_DELETE:
+			if (change->data.tp.oldtuple)
+			{
+				OutputPluginPrepareWrite(ctx, true);
+				logicalrep_write_delete(ctx->out, relation,
+										&change->data.tp.oldtuple->tuple);
+				OutputPluginWrite(ctx, true);
+			}
+			else
+				elog(DEBUG1, "didn't send DELETE change because of missing oldtuple");
+			break;
+		default:
+			Assert(false);
+	}
+
+	/* Cleanup */
+	MemoryContextSwitchTo(old);
+	MemoryContextReset(data->context);
+}
+
+/*
+ * Currently we always forward.
+ */
+static bool
+pgoutput_origin_filter(LogicalDecodingContext *ctx,
+						RepOriginId origin_id)
+{
+	return false;
+}
+
+/*
+ * Shutdown the output plugin.
+ *
+ * Note, we don't need to clean the data->context as it's child context
+ * of the ctx->context so it will be cleaned up by logical decoding machinery.
+ */
+static void
+pgoutput_shutdown(LogicalDecodingContext * ctx)
+{
+	if (RelationSyncCache)
+	{
+		hash_destroy(RelationSyncCache);
+		RelationSyncCache = NULL;
+	}
+}
+
+/*
+ * Load publications from the list of publication names.
+ */
+static List *
+LoadPublications(List *pubnames)
+{
+	List	   *result = NIL;
+	ListCell   *lc;
+
+	foreach (lc, pubnames)
+	{
+		char		   *pubname = (char *) lfirst(lc);
+		Publication	   *pub = GetPublicationByName(pubname, false);
+
+		result = lappend(result, pub);
+	}
+
+	return result;
+}
+
+/*
+ * Publication cache invalidation callback.
+ */
+static void
+publication_invalidation_cb(Datum arg, int cacheid, uint32 hashvalue)
+{
+	publications_valid = false;
+
+	/*
+	 * Also invalidate per-relation cache so that next time the filtering
+	 * info is checked it will be updated with the new publication
+	 * settings.
+	 */
+	rel_sync_cache_publication_cb(arg, cacheid, hashvalue);
+}
+
+/*
+ * Initialize the relation schema sync cache for a decoding session.
+ *
+ * The hash table is destoyed at the end of a decoding session. While
+ * relcache invalidations still exist and will still be invoked, they
+ * will just see the null hash table global and take no action.
+ */
+static void
+init_rel_sync_cache(MemoryContext cachectx)
+{
+	HASHCTL	ctl;
+	MemoryContext old_ctxt;
+
+	if (RelationSyncCache != NULL)
+		return;
+
+	/* Make a new hash table for the cache */
+	MemSet(&ctl, 0, sizeof(ctl));
+	ctl.keysize = sizeof(Oid);
+	ctl.entrysize = sizeof(RelationSyncEntry);
+	ctl.hcxt = cachectx;
+
+	old_ctxt = MemoryContextSwitchTo(cachectx);
+	RelationSyncCache = hash_create("logical replication output relation cache",
+									128, &ctl,
+									HASH_ELEM | HASH_CONTEXT | HASH_BLOBS);
+	(void) MemoryContextSwitchTo(old_ctxt);
+
+	Assert(RelationSyncCache != NULL);
+
+	CacheRegisterRelcacheCallback(rel_sync_cache_relation_cb, (Datum) 0);
+	CacheRegisterSyscacheCallback(PUBLICATIONRELMAP,
+								  rel_sync_cache_publication_cb,
+								  (Datum) 0);
+}
+
+/*
+ * Find or create entry in the relation schema cache.
+ */
+static RelationSyncEntry *
+get_rel_sync_entry(PGOutputData *data, Oid relid)
+{
+	RelationSyncEntry  *entry;
+	bool				found;
+	MemoryContext		oldctx;
+
+	Assert(RelationSyncCache != NULL);
+
+	/* Find cached function info, creating if not found */
+	oldctx = MemoryContextSwitchTo(CacheMemoryContext);
+	entry = (RelationSyncEntry *) hash_search(RelationSyncCache,
+											  (void *) &relid,
+											  HASH_ENTER, &found);
+	MemoryContextSwitchTo(oldctx);
+	Assert(entry != NULL);
+
+	/* Not found means schema wasn't sent */
+	if (!found || !entry->replicate_valid)
+	{
+		List	   *pubids = GetRelationPublications(relid);
+		ListCell   *lc;
+
+		/* Reload publications if needed before use. */
+		if (!publications_valid)
+		{
+			oldctx = MemoryContextSwitchTo(CacheMemoryContext);
+			if (data->publications)
+				list_free_deep(data->publications);
+
+			data->publications = LoadPublications(data->publication_names);
+			MemoryContextSwitchTo(oldctx);
+			publications_valid = true;
+		}
+
+		/*
+		 * Build publication cache. We can't use one provided by relcache
+		 * as relcache considers all publications given relation is in, but
+		 * here we only need to consider ones that the subscriber requested.
+		 */
+		entry->pubactions.pubinsert = entry->pubactions.pubupdate =
+			entry->pubactions.pubdelete = false;
+
+		foreach(lc, data->publications)
+		{
+			Publication *pub = lfirst(lc);
+
+			if (pub->alltables || list_member_oid(pubids, pub->oid))
+			{
+				entry->pubactions.pubinsert |= pub->pubactions.pubinsert;
+				entry->pubactions.pubupdate |= pub->pubactions.pubupdate;
+				entry->pubactions.pubdelete |= pub->pubactions.pubdelete;
+			}
+
+			if (entry->pubactions.pubinsert && entry->pubactions.pubupdate &&
+				entry->pubactions.pubdelete)
+				break;
+		}
+
+		list_free(pubids);
+
+		entry->replicate_valid = true;
+	}
+
+	if (!found)
+		entry->schema_sent = false;
+
+	return entry;
+}
+
+/*
+ * Relcache invalidation callback
+ */
+static void
+rel_sync_cache_relation_cb(Datum arg, Oid relid)
+{
+	RelationSyncEntry  *entry;
+
+	/*
+	 * We can get here if the plugin was used in SQL interface as the
+	 * RelSchemaSyncCache is detroyed when the decoding finishes, but there
+	 * is no way to unregister the relcache invalidation callback.
+	 */
+	if (RelationSyncCache == NULL)
+		return;
+
+	/*
+	 * Nobody keeps pointers to entries in this hash table around outside
+	 * logical decoding callback calls - but invalidation events can come in
+	 * *during* a callback if we access the relcache in the callback. Because
+	 * of that we must mark the cache entry as invalid but not remove it from
+	 * the hash while it could still be referenced, then prune it at a later
+	 * safe point.
+	 *
+	 * Getting invalidations for relations that aren't in the table is
+	 * entirely normal, since there's no way to unregister for an
+	 * invalidation event. So we don't care if it's found or not.
+	 */
+	entry = (RelationSyncEntry *) hash_search(RelationSyncCache, &relid,
+											  HASH_FIND, NULL);
+
+	/*
+	 * Reset schema sent status as the relation definition may have
+	 * changed.
+	 */
+	if (entry != NULL)
+		entry->schema_sent = false;
+}
+
+/*
+ * Publication relation map syscache invalidation callback
+ */
+static void
+rel_sync_cache_publication_cb(Datum arg, int cacheid, uint32 hashvalue)
+{
+	HASH_SEQ_STATUS		status;
+	RelationSyncEntry  *entry;
+
+	/*
+	 * We can get here if the plugin was used in SQL interface as the
+	 * RelSchemaSyncCache is detroyed when the decoding finishes, but there
+	 * is no way to unregister the relcache invalidation callback.
+	 */
+	if (RelationSyncCache == NULL)
+		return;
+
+	/*
+	 * There is no way to find which entry in our cache the hash belongs to
+	 * so mark the whole cache as invalid.
+	 */
+	hash_seq_init(&status, RelationSyncCache);
+	while ((entry = (RelationSyncEntry *) hash_seq_search(&status)) != NULL)
+		entry->replicate_valid = false;
+}