Index size are not availlable with pg_relation_size about pgroonga

[ryusei145]

I think when you make PGroonga index, system creates some Postgres objects and Groonga objects. pg_relation_size function returns Postgres objects size as 0 but you can get Groonga objects size as shown below.

1. Retrieve relindex id for PGroonga index.
2. Retrieve Grronga object names using object_list command
   (I can get Groonga table object name and column object name by pgroonga_table_name()/pgroonga_index_column_name() function but I could not get any other object names.)
3. Retrieve Groonga object disk usage using object_inspect command (Groonga) and pgroonga_command() function (PGroonga ) for each objects you get at 2.

postgres=# \d test;
                       Table "public.test"
 Column |         Type          | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
 col1   | character varying(20) |           |          |
 col2   | character varying(20) |           |          |
 col3   | character varying(30) |           |          |
Indexes:
    "test_idx" pgroonga (col1, col2)

postgres=# select i.relname, ix.indexrelid from pg_index ix inner join pg_class as i on i.oid = ix.indexrelid where i.relname = 'test_idx';
 relname  | indexrelid
----------+------------
 test_idx |      17190
(1 row)

postgres=# select key, value->'path' from json_each(pgroonga_command('object_list')::json->1) where key like '%17190%';
         key          |       ?column?
----------------------+-----------------------
 Sources17190         | "base/5/pgrn.0000149"
 Lexicon17190_0       | "base/5/pgrn.000014A"
 Sources17190.col1    | "base/5/pgrn.000014B"
 Lexicon17190_0.index | "base/5/pgrn.000014C"
 Lexicon17190_1       | "base/5/pgrn.000014D"
 Sources17190.col2    | "base/5/pgrn.000014E"
 Lexicon17190_1.index | "base/5/pgrn.000014F"
(7 rows)

postgres=# select pgroonga_command('object_inspect Sources17190')::json->1->'disk_usage';
 ?column?
----------
 12648448
(1 row)

[hiroyuki-sato]

@rodo

A few month ago, I asked same question.

There are no index size command for pgroonga yet.
Alternatively, you can calculate index size with du command.

du -sk ${PGDATA}/base/${DB_ID}/pgrn*

Maybe that command will be introduce.
ie. pgroonga.disk_usage(index_name)

[rodo]

@hiroyuki-sato thanks a lot for you answer, I'll do calculate this way.

[warflash]

Hey 👋
Is there any update on this? I feel like getting easy and accurate index sizes would be a very nice addition. Especially since (atleast in my experience) fulltext indices tend to harder to predict when it comes to their size