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

On Tue, May 3, 2016 at 8:09 PM, 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?
>

It's look easy to reproduce.
I can send a sample dataset for analyze.

drop table if exists test;
create table test (custom_fields jsonb);
create index test_gin_key on test USING GIN(custom_fields);
insert into test select custom_fields from public.learners;
INSERT 0 1000000
\di+ test_gin_key
List of relations
Schema | Name | Type | Owner | Table | Size | Description
--------+--------------+-------+----------+-------+---------+-------------
public | test_gin_key | index | postgres | test | 4211 MB |

reindex index test_gin_key;

\di+ test_gin_key
List of relations
Schema | Name | Type | Owner | Table | Size | Description
--------+--------------+-------+----------+-------+--------+-------------
public | test_gin_key | index | postgres | test | 295 MB |

​

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

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