Re: Database size stays constant but disk space keeps shrinking -- postgres 9.1

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We had a situation where external sort was creating a humungous temp file and the space was reclaimed when the process was completed.

Thanks.
Dinesh

On 9/28/2012 8:59 AM, Steve Crawford wrote:
On 09/27/2012 07:01 PM, Greg Williamson wrote:
Steve (and others who replied):
...
The other is a slimmed-down version of our production database, which gets
recreated hourly by a shell script which pulls data from remote servers, does a
pg_dump of the resulting 3 gig database, and then drops it.
...

Could you explain this process in more detail? Are you creating a new database, reading in data, dumping then dropping the whole database or just manipulating tables within an existing database?

Have you checked to see if there are any processes that have open handles to deleted files (lsof -X | grep deleted). Deleted files won't show up in du but won't release their disk space until the process exits. Perhaps a script or scripts, even one of your hourly ones, that terminate when the server restarts? You could save the output of lsof and ps immediately before and after
a restart and compare them.
lsof -X | grep deleted | wc -l

shows: 835 such files.

A couple:
postgres 2540 postgres 50u REG 8,3 409600 93429 /var/lib/postgresql/9.1/main/base/2789
200/11816 (deleted)
postgres 2540 postgres 51u REG 8,3 18112512 49694570 /var/lib/postgresql/9.1/main/base/2789
200/2791679 (deleted)
<...>...
I'll leave it to you and Tom to puzzle over the the postgres-related open files. Meanwhile, I'm a bit curious about the other 800+ and whether they are associated with scripts or processes that are connected to PostgreSQL.

First, what is the output of "select * from pg_stat_activity;"? Are there connections you don't expect to see? If you force any of them closed (after checking with anyone who may be impacted), do you see any file handles released or disk-space freed?

Second, do any of the processes associated with the other open-but-deleted files relate to programs or scripts that connect to PostgreSQL? Next time you do a restart, do any of the processes exit or do any of the deleted files get closed?

I'm wondering if you have processes that connect to PostgreSQL which terminate and release their file-handles when PG is restarted.

Cheers,
Steve






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