Re: Errors on missing pg_subtrans/ files with 9.3

On Tue, Nov 12, 2013 at 11:55 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> Hi,
>
> On 2013-11-12 11:46:19 -0500, J Smith wrote:
>> > * Does SELECT count(*) FROM pg_prepared_xacts; return 0?
>>
>> Yes it does.
>
> Could you show the output? Do you actually use prepared xacts actively?

jay:dev(at)jagger=# select * from pg_prepared_xacts;
transaction | gid | prepared | owner | database
-------------+-----+----------+-------+----------
(0 rows)

We don't actively use prepared transactions, no. We use a lot of
prepared statements, but no two-phase committing.

> Do you actively use row level locking?

Not to my knowledge, no. I've enabled statement logging for a little
while so we can get a snapshot of what our average queries look like,
but I'm not seeing any PREPARE TRANSACTION or explicit LOCK
statements.

> Is there high concurrency in that environment? In short, could you describe your database usage a bit?

This particular database is used for an aggregation service. There are
a handful of Hibernate-based Java processes that manipulate and
massage the data from a number of data feeds we receive 24-7 From a
quick grepping of the statement log file we captured the following
over the course of approximately 13 minutes:

167452 SELECTs
72388 UPDATEs
6782 INSERTs
2 DELETEs

> Did you restart the database since getting the errors?

Yes, we've restarted several times.

>> Latest checkpoint's NextXID: 0/5138174
>> Latest checkpoint's NextOID: 3574036
>> Latest checkpoint's NextMultiXactId: 5762623
>> Latest checkpoint's NextMultiOffset: 11956824
>> Latest checkpoint's oldestXID: 1673
>> Latest checkpoint's oldestXID's DB: 1
>> Latest checkpoint's oldestActiveXID: 5138174
>> Latest checkpoint's oldestMultiXid: 1
>
> Interesting. Pretty high multixact usage.
>

Part of our process involves a collecting several records and
aggregating them within a single transaction. There will usually be a
handful of SELECTs to fetch the data, a bit of processing in the Java
backend, then a set of either UPDATEs or INSERTs into two tables to
store the results of the processing or in rarer cases a couple of
DELETEs.

Our Java guy would have more details, as I just have the output of the
log files and a high-level view of how our backend processes work, but
this is the general gist of things as I understand it.

Cheers