logical decoding: process ASSIGNMENT during snapshot build

Most WAL records are ignored in early SnapBuild snapshot build phases.
But it's critical to process some of them, so that later messages have
the correct transaction state after the snapshot is completely built; in
particular, XLOG_XACT_ASSIGNMENT messages are critical in order for
sub-transactions to be correctly assigned to their parent transactions,
or at least one assert misbehaves, as reported by Ildar Musin.

Diagnosed-by: Masahiko Sawada
Author: Masahiko Sawada
Discussion: https://postgr.es/m/CAONYFtOv+Er1p3WAuwUsy1zsCFrSYvpHLhapC_fMD-zNaRWxYg@mail.gmail.com

diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 5315d93af06361282483aa00ba87a99f0ec48186..c53e7e227988616b907b21347a92a729febb554d 100644 (file)
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -217,12 +217,15 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
        uint8           info = XLogRecGetInfo(r) & XLOG_XACT_OPMASK;
 
        /*
-        * No point in doing anything yet, data could not be decoded anyway. It's
-        * ok not to call ReorderBufferProcessXid() in that case, except in the
-        * assignment case there'll not be any later records with the same xid;
-        * and in the assignment case we'll not decode those xacts.
+        * If the snapshot isn't yet fully built, we cannot decode anything, so
+        * bail out.
+        *
+        * However, it's critical to process XLOG_XACT_ASSIGNMENT records even
+        * when the snapshot is being built: it is possible to get later records
+        * that require subxids to be properly assigned.
         */
-       if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
+       if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT &&
+               info != XLOG_XACT_ASSIGNMENT)
                return;
 
        switch (info)