Re: Insert only table and size of GIN index JSONB field.

On Wed, May 4, 2016 at 3:45 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> On Tue, May 3, 2016 at 3:09 AM, Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com> wrote:
> > Hi,
> >
> > I started with empty table with index over
> > custom_fields | jsonb
> > field
> > defined as:
> > "idx_learners_custom_fields" gin (custom_fields)
> > Globally gin_pending_list_limit set to 2MB.
> > Database version is 9.5.2.
> >
> > Now question:
> > If table populated with 1M records in single transaction then the final
> size
> > of the GIN index is:
> > 4265 MB
> > but after I performed reindex index idx_learners_custom_fields;
> > the index size had been reduced 15x to 295 MB.
> >
> > Is this behavior expected?
>
> This sounds like a known issue, fixed in 9.6, where the pages used for
> the pending list do not eligible for recycling until the table is
> vacuumed. Autovacuum does not run on insert only tables, so they just
> accumulate as empty pages in the index.
>
> Cheers,
>
> Jeff
>

​Hi Jeff,

Yes it's look like a cause.
Is there any workaround possible for 9.5.2?
At this moment I see palliative (because it doesn't reduce already bloated
index) cure via performing manual vacuum on the table after each batch
insert
or very slow (for the large table) full scale fix via create new index/drop
old index.
​

--
Maxim Boguk
Senior Postgresql DBA
http://www.postgresql-consulting.com/

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