Dexter
The automatic indexer for Postgres
Installation
First, install HypoPG on your database server. This doesn’t require a restart.
cd /tmp
curl -L https://github.com/HypoPG/hypopg/archive/1.2.0.tar.gz | tar xz
cd hypopg-1.2.0
make
make install # may need sudo
Note: If you have issues, make sure
postgresql-server-dev-*
is installed.
Enable logging for slow queries in your Postgres config file.
log_min_duration_statement = 10 # ms
And install the command line tool with:
gem install pgdexter
The command line tool is also available as a Linux package.
How to Use
Dexter needs a connection to your database and a log file to process.
tail -F -n +1 <log-file> | dexter <connection-options>
This finds slow queries and generates output like:
Started
Processing 189 new query fingerprints
Index found: public.genres_movies (genre_id)
Index found: public.genres_movies (movie_id)
Index found: public.movies (title)
Index found: public.ratings (movie_id)
Index found: public.ratings (rating)
Index found: public.ratings (user_id)
Processing 12 new query fingerprints
To be safe, Dexter will not create indexes unless you pass the --create
flag. In this case, you’ll see:
Index found: public.ratings (user_id)
Creating index: CREATE INDEX CONCURRENTLY ON "public"."ratings" ("user_id")
Index created: 15243 ms
Connection Options
Dexter supports the same connection options as psql.
-h host -U user -p 5432 -d dbname
This includes URIs:
postgresql://user:pass@host:5432/dbname
and connection strings:
host=localhost port=5432 dbname=mydb
Collecting Queries
There are many ways to collect queries. For real-time indexing, pipe your logfile:
tail -F -n +1 <log-file> | dexter <connection-options>
Pass a single statement with:
dexter <connection-options> -s "SELECT * FROM ..."
or pass files:
dexter <connection-options> <file1> <file2>
or collect running queries with:
dexter <connection-options> --pg-stat-activity
or use the pg_stat_statements extension:
dexter <connection-options> --pg-stat-statements
Note: Logs or running queries are highly preferred over pg_stat_statements, as pg_stat_statements often doesn’t store enough information to optimize queries.
Collection Options
To prevent one-off queries from being indexed, specify a minimum number of calls before a query is considered for indexing
dexter --min-calls 100
You can do the same for total time a query has run
dexter --min-time 10 # minutes
Specify the format
dexter --input-format csv
When streaming logs, specify the time to wait between processing queries
dexter --interval 60 # seconds
Examples
Ubuntu with PostgreSQL 12
tail -F -n +1 /var/log/postgresql/postgresql-12-main.log | sudo -u postgres dexter dbname
Homebrew on Mac
tail -F -n +1 /usr/local/var/postgres/server.log | dexter dbname
Analyze
For best results, make sure your tables have been recently analyzed so statistics are up-to-date. You can ask Dexter to analyze tables it comes across that haven’t been analyzed in the past hour with:
dexter --analyze
Tables
You can exclude large or write-heavy tables from indexing with:
dexter --exclude table1,table2
Alternatively, you can specify which tables to index with:
dexter --include table3,table4
Debugging
See how Dexter is processing queries with:
dexter --log-sql --log-level debug2
Hosted Postgres
Some hosted providers like Amazon RDS and Heroku do not support the HypoPG extension, which Dexter needs to run. See how to use Dexter in these cases.
Future Work
Upgrading
Run:
gem install pgdexter
To use master, run:
gem install specific_install
gem specific_install https://github.com/ankane/dexter.git
Thanks
This software wouldn’t be possible without HypoPG, which allows you to create hypothetical indexes, and pg_query, which allows you to parse and fingerprint queries. A big thanks to Dalibo and Lukas Fittl respectively.
Research
This is known as the Index Selection Problem (ISP).
Contributing
Everyone is encouraged to help improve this project. Here are a few ways you can help:
- Report bugs
- Fix bugs and submit pull requests
- Write, clarify, or fix documentation
- Suggest or add new features
To get started with development, run:
git clone https://github.com/ankane/dexter.git
cd dexter
bundle install
bundle exec rake install
To run tests, use:
createdb dexter_test
bundle exec rake test