Re: Avoiding unnecessary reads in recovery

Tom Lane wrote:
> Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
>> Tom Lane wrote:
>>> but it'd make it safe to use in non-WAL contexts (I think there are
>>> other places where we know we are going to init the page and so a
>>> physical read is a waste of time).
>
>> Is there? I can't think of any. Extending a relation doesn't count.
>
> No, but re-using a free page in an index does. I'm not sure which index
> AMs know for sure the page is free, and which have to read it and check,
> but I think there's at least some scope for that.

B-tree, GIN ans GiST read and check. I'm not sure how hash works. I
think the latest bitmap index patch doesn't support reusing empty pages
at all.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com