Introduce logical decoding.

This feature, building on previous commits, allows the write-ahead log
stream to be decoded into a series of logical changes; that is,
inserts, updates, and deletes and the transactions which contain them.
It is capable of handling decoding even across changes to the schema
of the effected tables.  The output format is controlled by a
so-called "output plugin"; an example is included.  To make use of
this in a real replication system, the output plugin will need to be
modified to produce output in the format appropriate to that system,
and to perform filtering.

Currently, information can be extracted from the logical decoding
system only via SQL; future commits will add the ability to stream
changes via walsender.

Andres Freund, with review and other contributions from many other
people, including Álvaro Herrera, Abhijit Menon-Sen, Peter Gheogegan,
Kevin Grittner, Robert Haas, Heikki Linnakangas, Fujii Masao, Abhijit
Menon-Sen, Michael Paquier, Simon Riggs, Craig Ringer, and Steve
Singer.

1 files changed, 34 insertions, 2 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index ad46eb0cebf..53a20b1e606 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -23,6 +23,7 @@
 
 #include "access/clog.h"
 #include "access/multixact.h"
+#include "access/rewriteheap.h"
 #include "access/subtrans.h"
 #include "access/timeline.h"
 #include "access/transam.h"
@@ -39,7 +40,9 @@
 #include "pgstat.h"
 #include "postmaster/bgwriter.h"
 #include "postmaster/startup.h"
+#include "replication/logical.h"
 #include "replication/slot.h"
+#include "replication/snapbuild.h"
 #include "replication/walreceiver.h"
 #include "replication/walsender.h"
 #include "storage/barrier.h"
@@ -4016,6 +4019,27 @@ CheckXLogRemoved(XLogSegNo segno, TimeLineID tli)
 }
 
 /*
+ * Return the last WAL segment removed, or 0 if no segment has been removed
+ * since startup.
+ *
+ * NB: the result can be out of date arbitrarily fast, the caller has to deal
+ * with that.
+ */
+XLogSegNo
+XLogGetLastRemovedSegno(void)
+{
+	/* use volatile pointer to prevent code rearrangement */
+	volatile XLogCtlData *xlogctl = XLogCtl;
+	XLogSegNo	lastRemovedSegNo;
+
+	SpinLockAcquire(&xlogctl->info_lck);
+	lastRemovedSegNo = xlogctl->lastRemovedSegNo;
+	SpinLockRelease(&xlogctl->info_lck);
+
+	return lastRemovedSegNo;
+}
+
+/*
  * Update the last removed segno pointer in shared memory, to reflect
  * that the given XLOG file has been removed.
  */
@@ -6559,6 +6583,12 @@ StartupXLOG(void)
 	StartupReplicationSlots(checkPoint.redo);
 
 	/*
+	 * Startup logical state, needs to be setup now so we have proper data
+	 * during crash recovery.
+	 */
+	StartupReorderBuffer();
+
+	/*
 	 * Startup MultiXact.  We need to do this early for two reasons: one
 	 * is that we might try to access multixacts when we do tuple freezing,
 	 * and the other is we need its state initialized because we attempt
@@ -8589,7 +8619,7 @@ CreateCheckPoint(int flags)
 	 * StartupSUBTRANS hasn't been called yet.
 	 */
 	if (!RecoveryInProgress())
-		TruncateSUBTRANS(GetOldestXmin(true, false));
+		TruncateSUBTRANS(GetOldestXmin(NULL, false));
 
 	/* Real work is done, but log and update stats before releasing lock. */
 	LogCheckpointEnd(false);
@@ -8674,6 +8704,8 @@ CheckPointGuts(XLogRecPtr checkPointRedo, int flags)
 	CheckPointPredicate();
 	CheckPointRelationMap();
 	CheckPointReplicationSlots();
+	CheckPointSnapBuild();
+	CheckPointLogicalRewriteHeap();
 	CheckPointBuffers(flags);	/* performs all required fsyncs */
 	/* We deliberately delay 2PC checkpointing as long as possible */
 	CheckPointTwoPhase(checkPointRedo);
@@ -8965,7 +8997,7 @@ CreateRestartPoint(int flags)
 	 * this because StartupSUBTRANS hasn't been called yet.
 	 */
 	if (EnableHotStandby)
-		TruncateSUBTRANS(GetOldestXmin(true, false));
+		TruncateSUBTRANS(GetOldestXmin(NULL, false));
 
 	/* Real work is done, but log and update before releasing lock. */
 	LogCheckpointEnd(true);