Re: Stalled post to pgsql-bugs

Sushant Sinha <sushant(at)indiankanoon(dot)com> wrote:
> On Thu, Jul 23, 2015 at 10:27 AM, <pgsql-bugs-owner(at)postgresql(dot)org> wrote:

>> After upgrade from postgres 9.4.3 to 9.4.4 I am seeing constant disk writes
>> of 4-8MB/s in the background in production. I verified it using iotop and
>> vmstat. iotop shows "Total Disk Write" to be minuscule (like 10-100Kbps). It
>> is affecting runtime performance. I never noticed this issue with postgres
>> 9.4.3.
>>
>> I increased the shared buffers from 128MB to 1GB and still didn't see any
>> benefit.
>>
>> The website (http://indiankanoon.org) mostly uses text search with gin index
>> and some logging of click through data. The main database is replicated
>> using "streaming asynchronous replication".
>>
>> I am going to downgrade it to 9.4.3 to see if the upgrade was the real
>> problem. But just wanted to check if anyone else noticed it.

> Ok. There is a problem with the patches that went in between
> Postgres 9.4.3->9.4.4
>
> I downgraded to Postgres 9.4.3 and everythig is normal. "Actual
> disk writes" in iostat is pretty much as "Total disk writes"
> (between 50-100 Kbps and not in Mbps). "vmstat 1" also shows no
> excessive disk writes.

Did you notice whether it was an autovacuum process causing the
additional I/O in 9.4.4? There were some bugs in 9.4.3 that failed
to vacuum away old multi-transaction tracking structures in a
timely fashion, causing data loss and database corruption. Once
you upgraded a background task was probably trying to make up for
the lack of timely maintenance, so that you would not experience
those problems. Downgrading may be a little faster for a little
while, but you're almost certain to regret doing it very soon....

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company