Re: fsm and vacuum

Le 02/12/2010 22:00, Little, Douglas a écrit :
> We're new to Greenplum, based on PG (8.2.13). we weren't advised to increase the max_fsm_relations switch as our db has grown.
> Currently we're nearly 14k tables/indexes and the switch is set to 1000.
> We've got it updated now, but wondering about the effect & recovery.
>
> We've regularly been reloading tables with CTAS.
> I've done some experiments and want to confirm my understanding.
>
> 1. Vacuum full only compacted the oldest? tables (reducing pages from 109 to 5)
> 2. vacuum full frees pages, but doesn't reduce the file size (newer tables). Table needed to be recreated to reduce size
>
> I've searched the archives and haven't found what I'm looking for. I hope someone would just dash off a simple explanation.
>
> 1. when are relations added to the fsm? (at create, or some other time)

During vacuum, if there are dead spaces in the table.

> 2. will vacuum (full) add a relation to the fsm - ?

Yes, for tables with dead spaces.

> 3. if bloated table is vacuum full'd, will the free space pages be use?

If vacuum full did its job, it shouldn't be.

> My assumptions are:
> 1. relation added to fsm list at create time.

Nope.

> 2. fsm_pages keep track of free space for the relations being tracked in the fsm_relation list

At vacuum time.

> 3. table recreate is the only way to have a relation tracked.

Nope.

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Guillaume
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