Extend the output plugin API to allow decoding of prepared xacts.

This adds six methods to the output plugin API, adding support for
streaming changes of two-phase transactions at prepare time.

* begin_prepare
* filter_prepare
* prepare
* commit_prepared
* rollback_prepared
* stream_prepare

Most of this is a simple extension of the existing methods, with the
semantic difference that the transaction is not yet committed and maybe
aborted later.

Until now two-phase transactions were translated into regular transactions
on the subscriber, and the GID was not forwarded to it. None of the
two-phase commands were communicated to the subscriber.

This patch provides the infrastructure for logical decoding plugins to be
informed of two-phase commands Like PREPARE TRANSACTION, COMMIT PREPARED
and ROLLBACK PREPARED commands with the corresponding GID.

This also extends the 'test_decoding' plugin, implementing these new
methods.

This commit simply adds these new APIs and the upcoming patch to "allow
the decoding at prepare time in ReorderBuffer" will use these APIs.

Author: Ajin Cherian and Amit Kapila based on previous work by Nikhil Sontakke and Stas Kelvich
Reviewed-by: Amit Kapila, Peter Smith, Sawada Masahiko, and Dilip Kumar
Discussion:
https://postgr.es/m/02DA5F5E-CECE-4D9C-8B4B-418077E2C010@postgrespro.ru
https://postgr.es/m/CAMGcDxeqEpWj3fTXwqhSwBdXd2RS9jzwWscO-XbeCfso6ts3+Q@mail.gmail.com

3 files changed, 103 insertions, 0 deletions

diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index 40bab7ee02d..28c9c1f474e 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -85,6 +85,11 @@ typedef struct LogicalDecodingContext
 	bool		streaming;
 
 	/*
+	 * Does the output plugin support two-phase decoding, and is it enabled?
+	 */
+	bool		twophase;
+
+	/*
 	 * State for writing output.
 	 */
 	bool		accept_writes;
@@ -120,6 +125,7 @@ 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_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id);
 extern void ResetLogicalStreamingState(void);
 extern void UpdateDecodingStats(LogicalDecodingContext *ctx);
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index b78c796450a..89e1dc3517d 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -100,6 +100,45 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (struct LogicalDecodingContext *ct
 typedef void (*LogicalDecodeShutdownCB) (struct LogicalDecodingContext *ctx);
 
 /*
+ * Called before decoding of PREPARE record to decide whether this
+ * transaction should be decoded with separate calls to prepare and
+ * commit_prepared/rollback_prepared callbacks or wait till COMMIT PREPARED
+ * and sent as usual transaction.
+ */
+typedef bool (*LogicalDecodeFilterPrepareCB) (struct LogicalDecodingContext *ctx,
+											  const char *gid);
+
+/*
+ * Callback called for every BEGIN of a prepared trnsaction.
+ */
+typedef void (*LogicalDecodeBeginPrepareCB) (struct LogicalDecodingContext *ctx,
+											 ReorderBufferTXN *txn);
+
+/*
+ * Called for PREPARE record unless it was filtered by filter_prepare()
+ * callback.
+ */
+typedef void (*LogicalDecodePrepareCB) (struct LogicalDecodingContext *ctx,
+										ReorderBufferTXN *txn,
+										XLogRecPtr prepare_lsn);
+
+/*
+ * Called for COMMIT PREPARED.
+ */
+typedef void (*LogicalDecodeCommitPreparedCB) (struct LogicalDecodingContext *ctx,
+											   ReorderBufferTXN *txn,
+											   XLogRecPtr commit_lsn);
+
+/*
+ * Called for ROLLBACK PREPARED.
+ */
+typedef void (*LogicalDecodeRollbackPreparedCB) (struct LogicalDecodingContext *ctx,
+												 ReorderBufferTXN *txn,
+												 XLogRecPtr prepare_end_lsn,
+												 TimestampTz prepare_time);
+
+
+/*
  * Called when starting to stream a block of changes from in-progress
  * transaction (may be called repeatedly, if it's streamed in multiple
  * chunks).
@@ -124,6 +163,14 @@ typedef void (*LogicalDecodeStreamAbortCB) (struct LogicalDecodingContext *ctx,
 											XLogRecPtr abort_lsn);
 
 /*
+ * Called to prepare changes streamed to remote node from in-progress
+ * transaction. This is called as part of a two-phase commit.
+ */
+typedef void (*LogicalDecodeStreamPrepareCB) (struct LogicalDecodingContext *ctx,
+											  ReorderBufferTXN *txn,
+											  XLogRecPtr prepare_lsn);
+
+/*
  * Called to apply changes streamed to remote node from in-progress
  * transaction.
  */
@@ -173,10 +220,19 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
+
+	/* streaming of changes at prepare time */
+	LogicalDecodeFilterPrepareCB filter_prepare_cb;
+	LogicalDecodeBeginPrepareCB begin_prepare_cb;
+	LogicalDecodePrepareCB prepare_cb;
+	LogicalDecodeCommitPreparedCB commit_prepared_cb;
+	LogicalDecodeRollbackPreparedCB rollback_prepared_cb;
+
 	/* streaming of changes */
 	LogicalDecodeStreamStartCB stream_start_cb;
 	LogicalDecodeStreamStopCB stream_stop_cb;
 	LogicalDecodeStreamAbortCB stream_abort_cb;
+	LogicalDecodeStreamPrepareCB stream_prepare_cb;
 	LogicalDecodeStreamCommitCB stream_commit_cb;
 	LogicalDecodeStreamChangeCB stream_change_cb;
 	LogicalDecodeStreamMessageCB stream_message_cb;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index bd9dd7ec676..1e60afe70f4 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -245,6 +245,12 @@ typedef struct ReorderBufferTXN
 	TransactionId toplevel_xid;
 
 	/*
+	 * Global transaction id required for identification of prepared
+	 * transactions.
+	 */
+	char	   *gid;
+
+	/*
 	 * LSN of the first data carrying, WAL record with knowledge about this
 	 * xid. This is allowed to *not* be first record adorned with this xid, if
 	 * the previous records aren't relevant for logical decoding.
@@ -418,6 +424,26 @@ typedef void (*ReorderBufferMessageCB) (ReorderBuffer *rb,
 										const char *prefix, Size sz,
 										const char *message);
 
+/* begin prepare callback signature */
+typedef void (*ReorderBufferBeginPrepareCB) (ReorderBuffer *rb,
+											 ReorderBufferTXN *txn);
+
+/* prepare callback signature */
+typedef void (*ReorderBufferPrepareCB) (ReorderBuffer *rb,
+										ReorderBufferTXN *txn,
+										XLogRecPtr prepare_lsn);
+
+/* commit prepared callback signature */
+typedef void (*ReorderBufferCommitPreparedCB) (ReorderBuffer *rb,
+											   ReorderBufferTXN *txn,
+											   XLogRecPtr commit_lsn);
+
+/* rollback  prepared callback signature */
+typedef void (*ReorderBufferRollbackPreparedCB) (ReorderBuffer *rb,
+												 ReorderBufferTXN *txn,
+												 XLogRecPtr prepare_end_lsn,
+												 TimestampTz prepare_time);
+
 /* start streaming transaction callback signature */
 typedef void (*ReorderBufferStreamStartCB) (
 											ReorderBuffer *rb,
@@ -436,6 +462,12 @@ typedef void (*ReorderBufferStreamAbortCB) (
 											ReorderBufferTXN *txn,
 											XLogRecPtr abort_lsn);
 
+/* prepare streamed transaction callback signature */
+typedef void (*ReorderBufferStreamPrepareCB) (
+											  ReorderBuffer *rb,
+											  ReorderBufferTXN *txn,
+											  XLogRecPtr prepare_lsn);
+
 /* commit streamed transaction callback signature */
 typedef void (*ReorderBufferStreamCommitCB) (
 											 ReorderBuffer *rb,
@@ -505,11 +537,20 @@ struct ReorderBuffer
 	ReorderBufferMessageCB message;
 
 	/*
+	 * Callbacks to be called when streaming a transaction at prepare time.
+	 */
+	ReorderBufferBeginCB begin_prepare;
+	ReorderBufferPrepareCB prepare;
+	ReorderBufferCommitPreparedCB commit_prepared;
+	ReorderBufferRollbackPreparedCB rollback_prepared;
+
+	/*
 	 * Callbacks to be called when streaming a transaction.
 	 */
 	ReorderBufferStreamStartCB stream_start;
 	ReorderBufferStreamStopCB stream_stop;
 	ReorderBufferStreamAbortCB stream_abort;
+	ReorderBufferStreamPrepareCB stream_prepare;
 	ReorderBufferStreamCommitCB stream_commit;
 	ReorderBufferStreamChangeCB stream_change;
 	ReorderBufferStreamMessageCB stream_message;