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

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От Christian Weyer
Тема Re: Unexpected (bad) performance when querying indexed JSONB column
Дата
Msg-id 7F9BEAD7-C190-4E21-8240-04687FA88435@thinktecture.com
обсуждение исходный текст
Список pgsql-performance
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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@postgresql.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.

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