Re: logical decoding - reading a user catalog table

On 11/17/2014 10:37 AM, Andres Freund wrote:
> On 2014-11-13 22:23:02 -0500, Steve Singer wrote:
>
>
> Also since updating (to 2c267e47afa4f9a7c) I've seen a assertion failure in
> a normal client connection, not the walsender
>
> #3 0x00000000006b4978 in GetSerializableTransactionSnapshotInt (
> snapshot=snapshot(at)entry=0xbfa8a0 <CurrentSnapshotData>,
> sourcexid=sourcexid(at)entry=0) at predicate.c:1738
> #4 0x00000000006b66c3 in GetSafeSnapshot (origSnapshot=<optimized out>)
> at predicate.c:1517
> #5 GetSerializableTransactionSnapshot (
> snapshot=0xbfa8a0 <CurrentSnapshotData>) at predicate.c:1598
> #6 0x00000000007d16dd in GetTransactionSnapshot () at snapmgr.c:200
> #7 0x00000000006c0e35 in exec_simple_query (
> query_string=0x1fd01b8 "select ev_origin, ev_seqno, ev_timestamp,
> ev_snapshot, \"pg_catalog\".txid_snapshot_xmin(ev_snapshot),
> \"pg_catalog\".txid_snapshot_xmax(ev_snapshot),
> coalesce(ev_provider_xid,\""...)
> at postgres.c:959
> #8 PostgresMain (argc=<optimized out>, argv=argv(at)entry=0x1f5ab50,
>
>
> I have no idea if this has anything to do with your recent changes or some
> other change. I haven't so far been able to replicate that since the first
> time I saw it.
> That crash is decidedly odd. Any chance you still have the full
> backtrace around?

Yes I still have the core file

>
> This is in the SSI code... I'm not immediately seeing how this could be
> related to logical decoding. It can't even be a imported snapshot,
> because the exported snapshot is marked repeatable read.
>
> Are you actually using serializable transactions? If so, how and why?

Yes, the test client that performs the 'simulated workload' does some
serializable transactions. It connects as a normal client via JDBC and
does a prepareStatement("SET TRANSACTION ISOLATION LEVEL SERIALIZABLE")
and then does some DML. Why? because it seemed like a good thing to
include in the test suite.

Your right this might have nothing to do with logical decoding. I
haven't been able to reproduce again either, I can't even say
if this problem was introduced to 9.4 in the past month or if it has
been around much longer and I just haven't hit it before.

>
> Greetings,
>
> Andres Freund
>