Add a xid argument to the filter_prepare callback for output plugins.

Along with gid, this provides a different way to identify the transaction.
The users that use xid in some way to prepare the transactions can use it
to filter prepare transactions. The later commands COMMIT PREPARED or
ROLLBACK PREPARED carries both identifiers, providing an output plugin the
choice of what to use.

Author: Markus Wanner
Reviewed-by: Vignesh C, Amit Kapila
Discussion: https://postgr.es/m/ee280000-7355-c4dc-e47b-2436e7be959c@enterprisedb.com

contrib/test_decoding/test_decoding.c

@@ -77,6 +77,7 @@ static void pg_decode_message(LogicalDecodingContext *ctx,
 							  bool transactional, const char *prefix,
 							  Size sz, const char *message);
 static bool pg_decode_filter_prepare(LogicalDecodingContext *ctx,
+									 TransactionId xid,
 									 const char *gid);
 static void pg_decode_begin_prepare_txn(LogicalDecodingContext *ctx,
 										ReorderBufferTXN *txn);
@@ -440,7 +441,8 @@ pg_decode_rollback_prepared_txn(LogicalDecodingContext *ctx,
  * substring, then we filter it out.
  */
 static bool
-pg_decode_filter_prepare(LogicalDecodingContext *ctx, const char *gid)
+pg_decode_filter_prepare(LogicalDecodingContext *ctx, TransactionId xid,
+						 const char *gid)
 {
 	if (strstr(gid, "_nodecode") != NULL)
 		return true;

doc/src/sgml/logicaldecoding.sgml

@@ -794,20 +794,25 @@ typedef void (*LogicalDecodeMessageCB) (struct LogicalDecodingContext *ctx,
        <command>COMMIT PREPARED</command> time. To signal that
        decoding should be skipped, return <literal>true</literal>;
        <literal>false</literal> otherwise. When the callback is not
-       defined, <literal>false</literal> is assumed (i.e. nothing is
-       filtered).
+       defined, <literal>false</literal> is assumed (i.e. no filtering, all
+       transactions using two-phase commit are decoded in two phases as well).
 <programlisting>
 typedef bool (*LogicalDecodeFilterPrepareCB) (struct LogicalDecodingContext *ctx,
+                                              TransactionId xid,
                                               const char *gid);
 </programlisting>
-      The <parameter>ctx</parameter> parameter has the same contents as for the
-      other callbacks. The <parameter>gid</parameter> is the identifier that later
-      identifies this transaction for <command>COMMIT PREPARED</command> or
-      <command>ROLLBACK PREPARED</command>.
+       The <parameter>ctx</parameter> parameter has the same contents as for
+       the other callbacks. The parameters <parameter>xid</parameter>
+       and <parameter>gid</parameter> provide two different ways to identify
+       the transaction.  The later <command>COMMIT PREPARED</command> or
+       <command>ROLLBACK PREPARED</command> carries both identifiers,
+       providing an output plugin the choice of what to use.
      </para>
      <para>
-      The callback has to provide the same static answer for a given
-      <parameter>gid</parameter> every time it is called.
+       The callback may be invoked multiple times per transaction to decode
+       and must provide the same static answer for a given pair of
+       <parameter>xid</parameter> and <parameter>gid</parameter> every time
+       it is called.
      </para>
      </sect3>
 
@@ -1219,9 +1224,11 @@ stream_commit_cb(...);  &lt;-- commit of the streamed transaction
    </para>
 
    <para>
-    Optionally the output plugin can specify a name pattern in the
-    <function>filter_prepare_cb</function> and transactions with gid containing
-    that name pattern will not be decoded as a two-phase commit transaction.
+    Optionally the output plugin can define filtering rules via
+    <function>filter_prepare_cb</function> to decode only specific transaction
+    in two phases.  This can be achieved by pattern matching on the
+    <parameter>gid</parameter> or via lookups using the
+    <parameter>xid</parameter>.
    </para>
 
    <para>

src/backend/replication/logical/decode.c

@@ -80,7 +80,8 @@ static void DecodePrepare(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
 static void DecodeXLogTuple(char *data, Size len, ReorderBufferTupleBuf *tup);
 
 /* helper functions for decoding transactions */
-static inline bool FilterPrepare(LogicalDecodingContext *ctx, const char *gid);
+static inline bool FilterPrepare(LogicalDecodingContext *ctx,
+								 TransactionId xid, const char *gid);
 static bool DecodeTXNNeedSkip(LogicalDecodingContext *ctx,
 							  XLogRecordBuffer *buf, Oid dbId,
 							  RepOriginId origin_id);
@@ -271,7 +272,8 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				 * doesn't filter the transaction at prepare time.
 				 */
 				if (info == XLOG_XACT_COMMIT_PREPARED)
-					two_phase = !(FilterPrepare(ctx, parsed.twophase_gid));
+					two_phase = !(FilterPrepare(ctx, xid,
+												parsed.twophase_gid));
 
 				DecodeCommit(ctx, buf, &parsed, xid, two_phase);
 				break;
@@ -298,7 +300,8 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				 * doesn't filter the transaction at prepare time.
 				 */
 				if (info == XLOG_XACT_ABORT_PREPARED)
-					two_phase = !(FilterPrepare(ctx, parsed.twophase_gid));
+					two_phase = !(FilterPrepare(ctx, xid,
+												parsed.twophase_gid));
 
 				DecodeAbort(ctx, buf, &parsed, xid, two_phase);
 				break;
@@ -355,7 +358,8 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				 * manner iff output plugin supports two-phase commits and
 				 * doesn't filter the transaction at prepare time.
 				 */
-				if (FilterPrepare(ctx, parsed.twophase_gid))
+				if (FilterPrepare(ctx, parsed.twophase_xid,
+								  parsed.twophase_gid))
 				{
 					ReorderBufferProcessXid(reorder, parsed.twophase_xid,
 											buf->origptr);
@@ -581,7 +585,8 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
  * this transaction as a regular commit later.
  */
 static inline bool
-FilterPrepare(LogicalDecodingContext *ctx, const char *gid)
+FilterPrepare(LogicalDecodingContext *ctx, TransactionId xid,
+			  const char *gid)
 {
 	/*
 	 * Skip if decoding of two-phase transactions at PREPARE time is not
@@ -599,7 +604,7 @@ FilterPrepare(LogicalDecodingContext *ctx, const char *gid)
 	if (ctx->callbacks.filter_prepare_cb == NULL)
 		return false;
 
-	return filter_prepare_cb_wrapper(ctx, gid);
+	return filter_prepare_cb_wrapper(ctx, xid, gid);
 }
 
 static inline bool

src/backend/replication/logical/logical.c

@@ -1083,7 +1083,8 @@ truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 }
 
 bool
-filter_prepare_cb_wrapper(LogicalDecodingContext *ctx, const char *gid)
+filter_prepare_cb_wrapper(LogicalDecodingContext *ctx, TransactionId xid,
+						  const char *gid)
 {
 	LogicalErrorCallbackState state;
 	ErrorContextCallback errcallback;
@@ -1104,7 +1105,7 @@ filter_prepare_cb_wrapper(LogicalDecodingContext *ctx, const char *gid)
 	ctx->accept_writes = false;
 
 	/* do the actual work: call callback */
-	ret = ctx->callbacks.filter_prepare_cb(ctx, gid);
+	ret = ctx->callbacks.filter_prepare_cb(ctx, xid, gid);
 
 	/* Pop the error context stack */
 	error_context_stack = errcallback.previous;

src/include/replication/logical.h

@@ -125,7 +125,8 @@ extern void LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn,
 												  XLogRecPtr restart_lsn);
 extern void LogicalConfirmReceivedLocation(XLogRecPtr lsn);
 
-extern bool filter_prepare_cb_wrapper(LogicalDecodingContext *ctx, const char *gid);
+extern bool filter_prepare_cb_wrapper(LogicalDecodingContext *ctx,
+									  TransactionId xid, const char *gid);
 extern bool filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id);
 extern void ResetLogicalStreamingState(void);
 extern void UpdateDecodingStats(LogicalDecodingContext *ctx);

src/include/replication/output_plugin.h

@@ -106,6 +106,7 @@ typedef void (*LogicalDecodeShutdownCB) (struct LogicalDecodingContext *ctx);
  * and sent as usual transaction.
  */
 typedef bool (*LogicalDecodeFilterPrepareCB) (struct LogicalDecodingContext *ctx,
+											  TransactionId xid,
 											  const char *gid);
 
 /*