Re: [COMMITTERS] pgsql: Avoid SnapshotResetXmin() during AtEOXact_Snapshot()

On Fri, Mar 24, 2017 at 12:27 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Mar 24, 2017 at 12:14 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Fri, Mar 24, 2017 at 10:23 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> Avoid SnapshotResetXmin() during AtEOXact_Snapshot()
>>>
>>> For normal commits and aborts we already reset PgXact->xmin
>>> Avoiding touching highly contented shmem improves concurrent
>>> performance.
>>>
>>> Simon Riggs
>>
>> I'm getting occasional crashes with backtraces that look like this:
>>
>> #4 0x0000000107e4be2b in AtEOXact_Snapshot (isCommit=<value
>> temporarily unavailable, due to optimizations>, isPrepare=0 '\0') at
>> snapmgr.c:1154
>> #5 0x0000000107a76c06 in CleanupTransaction () at xact.c:2643
>>
>> I suspect that is the fault of this patch. Please fix or revert.
>
> Also, the entire buildfarm is turning red.
>
> longfin, spurfowl, and magpie all show this assertion failure in the
> log. I haven't checked the others.
>
> TRAP: FailedAssertion("!(MyPgXact->xmin == 0)", File: "snapmgr.c", Line: 1154)

Another thing that is interesting is that when I run make -j8
check-world, the overall tests appear to succeed even though there are
failures mid-way through:

test tablefunc ... FAILED (test process exited with exit code 2)

...but then later we end with:

ok
All tests successful.
Files=11, Tests=80, 251 wallclock secs ( 0.07 usr 0.02 sys + 19.77
cusr 14.45 csys = 34.31 CPU)
Result: PASS

real 4m27.421s
user 3m50.047s
sys 1m31.937s

That's unrelated to the current problem of course, but it seems to
suggest that make's -j option doesn't entirely do what you'd expect
when used with make check-world.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company