On 05/15/2014 07:57 PM, Heikki Linnakangas wrote:
Spotted while testing pg_recvlogical:
Advertising
1. Set up pg_recvlogical to receive:
./pg_recvlogical -S fooslot -d postgres --create
./pg_recvlogical -S fooslot -d postgres --start -f -
2. In another terminal, with psql:
create table foo (id int4);
begin;
insert into foo values (4);
alter table foo alter column id type text;
prepare transaction 'foo';
commit prepared 'foo';
insert into foo values (1);
3. With current HEAD, after commit
bb38fb0d43c8d7ff54072bfd8bd63154e536b384, this produces an assertion
failure:
TRAP: FailedAssertion("!(((xid) != ((TransactionId) 0)))", File:
"reorderbuffer.c", Line: 508)
I believe that's we no longer assign another XID to the transaction that
does the COMMIT PREPARED. Previously, an extra XID, in addition to the
XID of the prepared transaction, was assigned for use in locking the
global transaction entry in shared memory, but that's no longer required.
However, even with that patch reverted, it doesn't work correctly:
ERROR: could not map filenode "base/12142/16390" to relation OID
LOG: starting logical decoding for slot fooslot
DETAIL: streaming transactions committing after 0/16D1670, reading WAL
from 0/16BC470
Ok, so the immediate cause was quick to find: when decoding a
commit-prepared WAL record, we have to use the XID from the record
content (patch attached). The XID in the record header is the XID of the
transaction doing the COMMIT PREPARED, which is always 0 after patch
bb38fb0d43c8d7ff54072bfd8bd63154e536b384 which causes the assertion. But
it was always wrong. After fixing, it no longer asserts or gives the
above "could not map filenode" error.
However, it still doesn't seem right. When I do the above as a regular
transaction, ie:
begin; insert into foo values (6); alter table foo alter column id type
text; commit;
pg_recvlogical prints this:
BEGIN 708
table public.foo: INSERT: id[text]:'6'
COMMIT 708
But if I do it as a prepared transaction:
begin; insert into foo values (7); alter table foo alter column id type
text; prepare transaction 'foo'; commit prepared 'foo';
pg_recvlogical prints nothing.
- Heikki
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index d6499d5..cc73652 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -225,7 +225,7 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
subxacts = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
invals = (SharedInvalidationMessage *) &(subxacts[xlrec->nsubxacts]);
- DecodeCommit(ctx, buf, prec->xl_xid, xlrec->dbId,
+ DecodeCommit(ctx, buf, prec->xid, xlrec->dbId,
xlrec->xact_time,
xlrec->nsubxacts, subxacts,
xlrec->nmsgs, invals);
--
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