Re: tracking commit timestamps

On Tue, Oct 22, 2013 at 5:16 PM, Alvaro Herrera
<alvherre@2ndquadrant.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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