Got to going this today, after a small delay due to the arrival of new
disks,
So the system is 2x700Mhz PIII, 512 Mb, Promise TX2000, 2x40G ATA-133
Maxtor Diamond+8 .
The relevent software is Freebsd 4.8 and Postgresql 7.4 Beta 2.
Two runs of 'pgbench -c 50 -t 1000000 -s 10 bench' with a power cord
removal after about 2 minutes were performed, one with hw.ata.wc = 1
(write cache enabled) and other with hw.ata.wc = 0 (disabled).
In *both* cases the Pg server survived - i.e it came up, performed
automatic recovery. Subsequent 'vacuum full' and further runs of pgbench
completed with no issues.
I would conclude that it not *always* the case that power failure
renders the database unuseable.
I have just noticed a similar posting from Scott were he finds the cache
enabled case has an dead database after power failure. It seems that
it's a question of how *likely* is it that the database will survive/not
survive a power failure...
The other interesting possibility is that Freebsd with soft updates
helped things remain salvageable in the cache enabled case (as some
writes *must* be lost at power off in this case)....
regards
Mark
scott.marlowe wrote:
>
>OK, but here's the real test. As the postgres user, run 'pgbench -i',
>then after that runs, run 'pgbench -c 50 -t 1000000'. While it's running
>and settled (pg aux|grep postgres|wc -l should show a number of ~54 or
>so.) pull the plug. Wait for the hard drives to spin down, then plug it
>back in and power it one. With SCSI you will still have a coherent
>database.
>
>
>
