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@entry=0xbfa8a0 <CurrentSnapshotData>,
>      sourcexid=sourcexid@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@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
orif it has 
 
been around much longer and I just haven't hit it before.




>
> Greetings,
>
> Andres Freund
>