Re: [COMMITTERS] pgsql: Keep track of transaction commit timestamps

Alex Shulgin <ash(at)commandprompt(dot)com> writes:
>
> Figured it out with a pg_usleep in bootstrap.c anyway. Does this look sane?
>
>
> DEBUG: inserting column 6 value "0"
> DEBUG: inserted -> 0
> DEBUG: inserting column 7 value "varchar_transform"
> TRAP: FailedAssertion("!(((xmax) >= ((TransactionId) 3)))", File: "/home/ash/src/postgresql/src/backend/storage/ipc/procarray.c", Line: 1414)

I've tried to debug this and I feel really dumbfound...

DEBUG: inserting column 7 value "varchar_transform"

Breakpoint 1, GetSnapshotData (snapshot=0xdb2d60 <CatalogSnapshotData>)
at /home/ash/src/postgresql/src/backend/storage/ipc/procarray.c:1413
1413 xmax = ShmemVariableCache->latestCompletedXid;

(gdb) p ShmemVariableCache->latestCompletedXid
$1 = 4294967295

(gdb) p *ShmemVariableCache
$2 = {nextOid = 10000, oidCount = 0, nextXid = 3, oldestXid = 3,
xidVacLimit = 200000003, xidWarnLimit = 2136483650,
xidStopLimit = 2146483650, xidWrapLimit = 2147483650, oldestXidDB = 1,
oldestCommitTs = 1, newestCommitTs = 0, latestCompletedXid = 4294967295}

(gdb) p xmax
$3 = 0

(gdb) n
1414 Assert(TransactionIdIsNormal(xmax));

(gdb) p xmax
$4 = 1

(gdb) p *ShmemVariableCache
$5 = {nextOid = 10000, oidCount = 0, nextXid = 3, oldestXid = 3,
xidVacLimit = 200000003, xidWarnLimit = 2136483650,
xidStopLimit = 2146483650, xidWrapLimit = 2147483650, oldestXidDB = 1,
oldestCommitTs = 1, newestCommitTs = 0, latestCompletedXid = 4294967295}

(gdb) p ShmemVariableCache->latestCompletedXid
$6 = 4294967295

(gdb)

How? Is there an another concurrent process with the old view of
VariableCacheData struct where latestCompletedXid still points to
oldestCommitTs?

This only happens with the CommitTs commit in effect.

--
Alex