Re: How to detect if a postgresql gin index is bloated

[Keith Fiske <keith.fiske@xxxxxxxxxxxxxxx>]

On Fri, Jul 26, 2024 at 6:49 AM khan Affan <bawag773@xxxxxxxxx> wrote:

The pgstattuple function provides the following useful columns:

• table_len: The length of the table.
• tuple_count: The number of tuples.
• tuple_len: The length of the tuples.
• dead_tuple_count: The number of dead tuples.
• dead_tuple_len: The length of dead tuples.
• free_space: The amount of free space.

Example

How you might use this function:

SELECT * FROM pgstattuple('gin_index_name');

Interpreting Results

• If the dead_tuple_count is high relative to the tuple_count, this indicates bloat.
• If free_space is a significant portion of table_len, the index may be bloated.

Using pg_trgm for Trigram Indexes

If you're using a GIN index with the pg_trgm extension (for trigram indexes), you might also consider analyzing the table and index sizes directly:

SELECT
  pg_size_pretty(pg_relation_size('table_name')) AS table_size,
  pg_size_pretty(pg_total_relation_size('table_name')) AS total_size,
  pg_size_pretty(pg_relation_size('gin_index_name')) AS index_size;

Vacuum and Reindex

If you determine that your GIN index is bloated, you can use VACUUM and REINDEX to reclaim space:

VACUUM ANALYZE your_table_name;
REINDEX INDEX your_gin_index_name;

By following these steps, you should be able to detect and address bloat in your PostgreSQL GIN indexes effectively.

Have you tried using that pgstattuple function with a GIN index?

postgres=# select * from pgstattuple('employees_systems_access');
ERROR:  "employees_systems_access" (gin index) is not supported 

There is a function specifically for them and it does not return the same info

postgres=# select * from pgstatginindex('employees_systems_access');
-[ RECORD 1 ]--+--
version        | 2
pending_pages  | 0
pending_tuples | 0

--

Keith Fiske
Senior Database Engineer
Crunchy Data - http://crunchydata.com