Re: pg_dump and pg_restore, speed

At 18:26 1/08/00 +0200, Kovacs Zoltan Sandor wrote:
>> Can you send me the actual times? And the command you used?
>I don't think my database is large enough to give you worthy data (~10000
>lines). But, with the old pg_dump I got 5 secs, with the new one: 9 secs.
>I used the -Fc option. The old dump was 377K, the new one is 285K.

The time diff and size diff is because the -Fc format compresses the data
by default. If you did '-Fc -Z0', you would get 0 compression, a larger
file, and a time that was closer to the original.

>pg_restore was fast, it was less than 1 sec. The total restoring time with
>psql was 29 secs from the old dump, 86 secs from the new one.

86 with the new one is a worry. It should not be that much slower - unless
there are a lot of tables, in which case updating of pg_class to disable
triggers for each table will slow it down a bit.

I assume from this that you used pg_restore to create a script, which you
then fed into psql. Is that right?

If so, you might like to try:

% createdb newdb
% pg_restore <backup-file> --db=newdb

this avoids using psql and should be faster. I'd be interested to know how
slow/fast it is. If it it still slow, is there any chance you could mail me
the backup file directly? I'll certainly understand if you say 'no', for
obvious reasons.

>I use Linux
>2.2-12.20 (RedHat 6.1), the server is a 366 MHz Intel Celeron with a
>WD64AA hard disk w/ 2048K cache.

Should be plenty.

>By the way, is there any statistics about the dumping/restoring time with
>larger databases? Is there a faster method to backup and restore a
>database than I did?

As above; dump: use -Z0 (no compression), restore: use --db to attach to
the DB directly.

Statistics I have done with databases of 100,000 records and 1.3M records
show no appreciable difference between the old & new for both dump &
restore. The dump always takes longer if compression is used. I have not
compared it to piping the output to gzip, but I imagine they are similar.

Hope this helps,

Philip.

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