Question about forced immediate checkpoints during create database

Hi everyone,

I have few question about checkpoints during create database.

First just extract from log on my test database 9.2.4:

2013-11-12 03:48:31 MSK 1717 @ from [vxid: txid:0] [] LOG: checkpoint
starting: immediate force wait
2013-11-12 03:48:31 MSK 1717 @ from [vxid: txid:0] [] LOG: checkpoint
complete: wrote 168 buffers (0.0%); 0 transaction log file(s) added, 0
removed, 0 recycled; write=0.314 s, sync=0.146 s, total=0.462 s; sync
files=104, longest=0.040 s, average=0.001 s
2013-11-12 03:48:32 MSK 1717 @ from [vxid: txid:0] [] LOG: checkpoint
starting: immediate force wait
2013-11-12 03:48:32 MSK 1717 @ from [vxid: txid:0] [] LOG: checkpoint
complete: wrote 6 buffers (0.0%); 0 transaction log file(s) added, 0
removed, 0 recycled; write=0.311 s, sync=0.002 s, total=0.315 s; sync
files=6, longest=0.000 s, average=0.000 s
2013-11-12 03:48:32 MSK 13609 postgres(at)hh_data from [local] [vxid:502/0
txid:0] [CREATE DATABASE] LOG: duration: 1160.409 ms statement: create
database _tmp;

So during creating of database two immediate force checkpoints was
performed.

Now questions:

1)Why these checkpoints performed at all? I understood why checkpoint
performed during drop database (to clean shared buffers from the dropped db
data), but why issue checkpoint during create database?

2)Why two checkpoints performed one after one?

3)Is there any good way to perform spread checkpoint during create database
(similar to --checkpoint=spread for the pg_basebackup) ?
I'm ready to wait 30 min for create database in that case...
I asking because performing immediate checkpoint on the large heavy loaded
database - good recipe for downtime (IO become overloaded to point of the
total stall)...
Is there any workaround for this problem?

4)Is idea to add an option for create/drop database syntax to control
checkpoint behaviour sounds reasonable?

Kind Regards,
Maksym

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Maxim Boguk
Senior Postgresql DBA
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