Re: tracking commit timestamps

On Tue, Oct 22, 2013 at 5:16 PM, Alvaro Herrera
<alvherre(at)2ndquadrant(dot)com> wrote:
> Hi,
>
> There has been some interest in keeping track of timestamp of
> transaction commits. This patch implements that.
>

Hi,

Sorry for the delay on the review.

First, because of the recent fixes the patch doesn't apply cleanly
anymore but the changes seems to be easy.

=== performance ===

i expected a regression on performance with the module turned on
because of the new XLOG records and wrote of files in pg_committs but
the performance drop is excessive.

Master 437.835674 tps
Patch, guc off 436.4340982 tps
Patch, guc on 0.370524 tps

This is in a pgbench's db initialized with scale=50 and run with
"pgbench -c 64 -j 16 -n -T 300" 5 times (values above are the average
of runs)

postgresql changes:

shared_buffers = 1GB
full_page_writes = off
checkpoint_segments = 30
checkpoint_timeout = 15min
random_page_cost = 2.0

== functionality ==

I started the server with the module off, then after some work turned
the module on and restarted the server and run a few benchs then
turned it off again and restart the server and get a message like:

"""
LOG: database system was not properly shut down; automatic recovery in progress
LOG: record with zero length at 0/3112AE58
LOG: redo is not required
FATAL: cannot make new WAL entries during recovery
LOG: startup process (PID 24876) exited with exit code 1
LOG: aborting startup due to startup process failure
"""

--
Jaime Casanova www.2ndQuadrant.com
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Phone: +593 4 5107566 Cell: +593 987171157