File: README — Documentation for pg_query

PostgreSQL Query Analyzer for Rails

Provides a PostgreSQL query analysis in your development logs.

This is useful for finding indexes that your database may benefit from. There are alternatives available that guess which indexes may help and provide example migrations, but I’ve found that performing a manual analysis using tools like this typically leads to the best results.

Instructions

Install the gem:

sudo gem install pg_query_analyzer

Require it development (config/enviroments/development.rb):

config.gem "pg_query_analyzer"

You’ll achieve the best results if you have your production database available locally. If you’re using Heroku (heroku.com) this means setting up your development database to use PostgreSQL and running (“heroku db:pull”).

Restart your server (“script/server” or “touch tmp/restart.txt”) and tail your development log (“tail -f -n 100 log/development.log”) to see the results. Note the “total runtime”, “cost”, and “actual time” data points to locate long running queries, as you might see in the second example provided below.

Once you identify which queries are worth optimizing, you can generate and run migrations to create the appropriate indexes, restart your server, and check your logs to ensure that you’re getting the results you expect. Once you’re finished, you can comment out or remove the config.gem call.

Example One

User Load (2.5ms)   SELECT * FROM "users" WHERE ("users"."id" = 2) LIMIT 1
Analyzing User Load Execution Time: 0.002899

Limit  (cost=0.00..8.27 rows=1 width=3734) (actual time=0.012..0.012 rows=1 loops=1)
Output: id, login, posts_count, followings_count, followers_count, created_at, updated_at,...
->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=3734) (actual time=0.011..0.011 rows=1 loops=1)
      Output: id, login, posts_count, followings_count, followers_count, created_at, updated_at...
      Index Cond: (id = 2)
Total runtime: 0.052 ms

Example Two

FeedItem Load (5.1ms)   SELECT * FROM "feed_items" WHERE ("feed_items".user_id = 2) ORDER BY feed_items.post_created_at DESC
Analyzing FeedItem Load Execution Time: 0.014169

Sort  (cost=248.49..249.21 rows=290 width=32) (actual time=1.870..1.895 rows=290 loops=1)
Output: id, user_id, post_id, poster_id, post_created_at, created_at
Sort Key: post_created_at
Sort Method:  quicksort  Memory: 47kB
->  Seq Scan on feed_items  (cost=0.00..236.62 rows=290 width=32) (actual time=0.015..1.735 rows=290 loops=1)
      Output: id, user_id, post_id, poster_id, post_created_at, created_at
      Filter: (user_id = 2)

Total runtime: 1.948 ms

Credits

MODIFIED by John Eberly originally take from svn.nfectio.us PostgreSQL and Oracle Adapter from Luca Mearelli spazidigitali.com Cooked and gemified by Marcos Piccinini github.com/nofxx/query-analyzer PostgreSQL Only Version from Trevor Turk github.com/trevorturk/pg_query_analyzer

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.