Re: Better tracking of free space during SP-GiST index build

On Sat, Sep 24, 2016 at 11:32 PM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
> On 09/22/2016 07:37 PM, Tom Lane wrote:
>>
>> Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
>>
>>> ... I've tried increasing the cache size to 768
>>> entries, with vast majority of them (~600) allocated to leaf pages.
>>> Sadly, this seems to only increase the CREATE INDEX duration a bit,
>>> without making the index significantly smaller (still ~120MB).
>>
>>
>> Yeah, that's in line with my results: not much further gain from a
>> larger cache.  Though if you were testing with the same IRRExplorer
>> data, it's not surprising that our results would match.  Would be
>> good to try some other cases...
>>
>
> Agreed, but I don't have any other data sets at hand. One possibility would
> be to generate something randomly (e.g. it's not particularly difficult to
> generate random IP addresses), but I'd much rather use some real-world data
> sets.

Tomas, I have one real dataset, which I used for testing spgist
(https://www.postgresql.org/message-id/CAF4Au4zxd2XOV0A__FU7xoHxSiwJzm1z2xhs-FFaT1DzB9ub3Q@mail.gmail.com)
Let me know if you need it.

>
>>>
>>>
>>> One thing I'd change is making the SpGistLUPCache dynamic, i.e.
>>> storing the size and lastUsedPagesMap on the meta page. That
>>> should allow us resizing the cache and tweak lastUsedPagesMap in
>>> the future.
>>
>>
>> Yeah, probably a good idea. I had thought of bumping
>> SPGIST_MAGIC_NUMBER again if we want to revisit the cache size; but
>> keeping it as a separate field won't add noticeable cost, and it
>> might save some trouble.
>>
>
> I see you plan to track only the cache size, while I proposed to track also
> the map, i.e. number of pages per category. I think that'd useful in case we
> come up with better values (e.g. more entries for leaf pages), or even
> somewhat adaptive way.
>
> regards
>
> --
> Tomas Vondra                  http://www.2ndQuadrant.com
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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