Thread: Multiple table scans to analyze multiple indexes

Hi all,

I might not be understanding this correctly, but does Postgres, when
VACUUM ANALYZE-ing a table, perform separate scans for each index?
And if so, is this necessary?  Can't it update indexes parallel?  This
would be particularly useful when rebuilding all indexes on a table.

Thanks

Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935

Thom Brown wrote:
> Hi all,
>
> I might not be understanding this correctly, but does Postgres, when
> VACUUM ANALYZE-ing a table, perform separate scans for each index?
> And if so, is this necessary?  Can't it update indexes parallel?  This
> would be particularly useful when rebuilding all indexes on a table.

Uh, I am unsure of the question.  ANALYZE randomly samples the heap,
plus generates analyze statistics for each expression index.

As far as VACUUM, that scans the heap and then scans the indexes based on
the free space is finds;  see vacuumlazy.c:


http://git.postgresql.org/gitweb?p=postgresql.git;a=blob;f=src/backend/commands/vacuumlazy.c;h=0ac993f957d6e49c23448dd85f8ed41308dc9c60;hb=HEAD

Are you asking why normal delete doesn't update the index?

This is probably a question for the hackers list.

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