Re: GUC for cleanup indexes threshold.

On Fri, Feb 10, 2017 at 8:01 PM, Kuntal Ghosh
<kuntalghosh(dot)2007(at)gmail(dot)com> wrote:
> On Wed, Jan 4, 2017 at 1:51 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
>> Attached patch introduces new GUC parameter parameter
>> vacuum_cleanup_index_scale_factor which specifies the fraction of the
>> table pages containing dead tuple needed to trigger a cleaning up
>> indexes. The default is 0.0, which means that the cleanup index is not
>> invoked if no update on table. In other word, if table is completely
>> frozen then lazy vacuum can skip the index scans as well. Increasing
>> this value could reduce total time of lazy vacuum but the statistics
>> and the free space map of index are not updated.
>>
> I was looking into your patch and trying to understand how the
> following piece of code works.

Thank you for looking at this patch!

> + if (vacuumed_pages > cleanupidx_thresh)
> + {
> + for (i = 0; i < nindexes; i++)
> + lazy_cleanup_index(Irel[i], indstats[i], vacrelstats);
> + }
> So, you are skipping deletion of index entries if it does not reach
> the clean-up index threshold. But, you are removing all dead tuples
> from the heap pointed by the same index. Hence, index will contain
> entries with invalid references.

I think no. Before calling lazy_cleanup_index, all garbage on heap and
index should have been reclaimed by lazy_vacuum_heap and
lazy_vacuum_index.

> + This parameter can only be set anywhere.
> Oxymoron. :-)
>

Will fix it.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center