On 2019-Jul-09, Masahiko Sawada wrote: > I think the cause of this bug would be that a ReorderBufferTXN entry > of sub transaction is created as top-level transaction. And this > happens because we skip to decode ASSIGNMENT during the state of > snapshot builder < SNAPBUILD_FULL.
That explanation seems to make sense. > Instead, I wonder if we can decode ASSIGNMENT even when the state of > snapshot builder < SNAPBUILD_FULL_SNAPSHOT. That way, the > ReorderBufferTXN entries of both top transaction and sub transaction > are created properly before we decode NEW_CID. Yeah, that seems a sensible remediation to me. I would reduce the scope a little bit -- only create the assignment in the BUILDING state, and skip it in the START state. I'm not sure that it's possible to get assignments while in START state that are significant (I'm still trying to digest SnapBuildFindSnapshot). I would propose the attached. Andres, do you have an opinion on this? -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>From 0d37a9a64bc20414742a8e9497dc8dffeeea16d1 Mon Sep 17 00:00:00 2001 From: Alvaro Herrera <alvhe...@alvh.no-ip.org> Date: Fri, 26 Jul 2019 18:38:44 -0400 Subject: [PATCH v3] decode XACT_ASSIGNMENT while building snapshot --- src/backend/replication/logical/decode.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c index 151c3ef882..a6f7dc2723 100644 --- a/src/backend/replication/logical/decode.c +++ b/src/backend/replication/logical/decode.c @@ -215,14 +215,19 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf) ReorderBuffer *reorder = ctx->reorder; XLogReaderState *r = buf->record; uint8 info = XLogRecGetInfo(r) & XLOG_XACT_OPMASK; + SnapBuildState state; /* - * 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) + state = SnapBuildCurrentState(builder); + if (state < SNAPBUILD_FULL_SNAPSHOT || + (info == XLOG_XACT_ASSIGNMENT && state < SNAPBUILD_BUILDING_SNAPSHOT)) return; switch (info) -- 2.17.1
