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Re: Errors on missing pg_subtrans/ files with 9.3

From: J Smith <dark(dot)panda+lists(at)gmail(dot)com>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Errors on missing pg_subtrans/ files with 9.3
Date: 2013-11-12 18:45:01
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Lists: pgsql-hackers
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

> 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

> 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

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.


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