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

[Maxim Boguk <maxim.boguk@xxxxxxxxx>]

On Tue, May 3, 2016 at 8:09 PM, Maxim Boguk <maxim.boguk@xxxxxxxxx> 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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