Re: race condition in sync rep

On Sat, Mar 26, 2011 at 12:41 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> Is it? Sync rep requires fsync on the standby. If you then explicitly
> turn off fsync on the standby then it has a performance impact, as
> documented.

Actually, it doesn't, now that you fixed this. Before:

[rhaas(at)office ~]$ pgbench -T 10
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 25
query mode: simple
number of clients: 1
number of threads: 1
duration: 10 s
number of transactions actually processed: 27
tps = 0.099386 (including connections establishing)
tps = 0.099389 (excluding connections establishing)
[rhaas(at)office ~]$ pgbench -T 10
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 25
query mode: simple
number of clients: 1
number of threads: 1
duration: 10 s
number of transactions actually processed: 425
tps = 42.442185 (including connections establishing)
tps = 42.468972 (excluding connections establishing)

The first one - run with code from a few weeks ago - hung up on the
27th transaction and was stuck there until the next checkpoint
completed. The second one was run with the latest code and no longer
hangs - and in fact it's now faster than running with fsync=on,
exactly as one would expect. Or at least as *I* expected.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company