Re: Unexpected (bad) performance when querying indexed JSONB column

Just checked: the execution time is the same when I drop the index.

Execution plan with index:
---
"Bitmap Heap Scan on articles (cost=16.25..135.64 rows=33 width=427)"
" Recheck Cond: (data @> '{"locked": true}'::jsonb)"
" -> Bitmap Index Scan on idx_data (cost=0.00..16.24 rows=33 width=0)"
" Index Cond: (data @> '{"locked": true}'::jsonb)"
---

And without the index:
---
"Seq Scan on articles (cost=0.00..2289.21 rows=33 width=427)"
" Filter: (data @> '{"locked": true}'::jsonb)"
---

-C.

From: Christian Weyer
Date: Samstag, 31. Januar 2015 17:00
To: "pgsql-performance(at)postgresql(dot)org<mailto:pgsql-performance(at)postgresql(dot)org>"
Subject: [PERFORM] Unexpected (bad) performance when querying indexed JSONB column

Hi all,

The pg version in question is the latest 9.4., running on Windows.

For testing out the NoSQL features of pg I have a simple table called ‘articles’ with a column called ‘data’.

There is an index on ‘data’ like this:
CREATE INDEX idx_data ON articles USING gin (data jsonb_path_ops);

The current test data set has 32570 entires of JSON docs like this:
{
"title": "Foo Bar",
"locked": true,
"valid_until": "2049-12-31T00:00:00",
"art_number": 12345678,
"valid_since": "2013-10-05T00:00:00",
"number_valid": false,
"combinations": {
"var1": "4711",
"var2": "4711",
"var3": "0815",
"int_art_number": "000001"
}
}

Nothing too complex, I think.

When I run a simple query:
SELECT data #>> ‘{"title"}'
FROM articles
WHERE data @> '{ “locked" : true }';

Reproducingly, it takes approx. 900ms to get the results back.
Honestly, I was expecting a much faster query.

Any opinions on this?

Thanks,
-C.