BUG #13515: Much higher disk writes after postgres upgrade 9.4.3->9.4.4

Sushant Sinha <sushant@indiankanoon.com> wrote:

On Thu, Jul 23, 2015 at 10:27 AM, <pgsql-bugs-owner@postgresql.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

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