# Rails PG Extras [![Gem Version](https://badge.fury.io/rb/rails-pg-extras.svg)](https://badge.fury.io/rb/rails-pg-extras) [![CircleCI](https://circleci.com/gh/pawurb/rails-pg-extras.svg?style=svg)](https://circleci.com/gh/pawurb/rails-pg-extras) Rails port of [Heroku PG Extras](https://github.com/heroku/heroku-pg-extras) with several additions and improvements. The goal of this project is to provide powerful insights into the PostgreSQL database for Ruby on Rails apps that are not using the Heroku PostgreSQL plugin. Included rake tasks and Ruby methods can be used to obtain information about a Postgres instance, that may be useful when analyzing performance issues. This includes information about locks, index usage, buffer cache hit ratios and vacuum statistics. Ruby API enables developers to easily integrate the tool into e.g. automatic monitoring tasks. You can read this blog post for detailed step by step tutorial on how to [optimize PostgreSQL using PG Extras library](https://pawelurbanek.com/postgresql-fix-performance). **Shameless plug:** rails-pg-extras is one of the tools that I use when conducting Rails performance audits. [Check out my offer](https://pawelurbanek.com/#rails-performance-tuning) if you need help with fine-tuning your app. Optionally you can enable a visual interface: ![Web interface](https://github.com/pawurb/rails-pg-extras/raw/master/pg-extras-ui.png) Alternative versions: - Core dependency - [Ruby](https://github.com/pawurb/ruby-pg-extras) - [NodeJS](https://github.com/pawurb/node-postgres-extras) - [Elixir](https://github.com/pawurb/ecto_psql_extras) - [Python Flask](https://github.com/nickjj/flask-pg-extras) - [Haskell](https://github.com/pawurb/haskell-pg-extras) ## Installation In your Gemfile ```ruby gem "rails-pg-extras" ``` `calls` and `outliers` queries require [pg_stat_statements](https://www.postgresql.org/docs/current/pgstatstatements.html) extension. You can check if it is enabled in your database by running: ```ruby RailsPgExtras.extensions ``` You should see the similar line in the output: ```bash | pg_stat_statements | 1.7 | 1.7 | track execution statistics of all SQL statements executed | ``` `ssl_used` requires `sslinfo` extension, and `buffercache_usage`/`buffercache_usage` queries need `pg_buffercache`. You can enable them all by running: ```ruby RailsPgExtras.add_extensions ``` By deafult a primary ActiveRecord database connection is used for running metadata queries, rake tasks and web UI. To connect to a different database you can specify an `ENV['RAILS_PG_EXTRAS_DATABASE_URL']` value in the following format: ```ruby ENV["RAILS_PG_EXTRAS_DATABASE_URL"] = "postgresql://postgres:secret@localhost:5432/database_name" ``` ## Usage Each command can be used as a rake task, or a directly from the Ruby code. ```bash rake pg_extras:cache_hit ``` ```ruby RailsPgExtras.cache_hit ``` ```bash +----------------+------------------------+ | Index and table hit rate | +----------------+------------------------+ | name | ratio | +----------------+------------------------+ | index hit rate | 0.97796610169491525424 | | table hit rate | 0.96724294813466787989 | +----------------+------------------------+ ``` By default the ASCII table is displayed, to change to format you need to specify the `in_format` parameter (`[:display_table, :hash, :array, :raw]` options are available): ```ruby RailsPgExtras.cache_hit(in_format: :hash) => [{"name"=>"index hit rate", "ratio"=>"0.97796610169491525424"}, {"name"=>"table hit rate", "ratio"=>"0.96724294813466787989"}] RailsPgExtras.cache_hit(in_format: :array) => [["index hit rate", "0.97796610169491525424"], ["table hit rate", "0.96724294813466787989"]] RailsPgExtras.cache_hit(in_format: :raw) => # ``` Some methods accept an optional `args` param allowing you to customize queries: ```ruby RailsPgExtras.long_running_queries(args: { threshold: "200 milliseconds" }) ``` ## Diagnose report The simplest way to start using pg-extras is to execute a `diagnose` method. It runs a set of checks and prints out a report highlighting areas that may require additional investigation: ```ruby RailsPgExtras.diagnose $ rake pg_extras:diagnose ``` ![Diagnose report](https://github.com/pawurb/rails-pg-extras/raw/master/rails-pg-extras-diagnose.png) Keep reading to learn about methods that `diagnose` uses under the hood. ## Visual interface You can enable UI using a Rails engine by adding the following code in `config/routes.rb`: ```ruby mount RailsPgExtras::Web::Engine, at: 'pg_extras' ``` You can enable HTTP basic auth by specifying `RAILS_PG_EXTRAS_USER` and `RAILS_PG_EXTRAS_PASSWORD` variables. Authentication is mandatory unless you specify `RAILS_PG_EXTRAS_PUBLIC_DASHBOARD=true` or setting `RailsPgExtras.configuration.public_dashboard` to `true`. You can configure available web actions in `config/initializers/rails_pg_extras.rb`: ```ruby RailsPgExtras.configure do |config| # Rails-pg-extras does not enable all the web actions by default. You can check all available actions via `RailsPgExtras::Web::ACTIONS`. # For example, you may want to enable the dangerous `kill_all` action. config.enabled_web_actions = %i[kill_all pg_stat_statements_reset add_extensions] end ``` ## Available methods ### `measure_queries` This method displays query types executed when running a provided Ruby snippet, with their avg., min., max., and total duration in miliseconds. It also outputs info about the snippet execution duration and the portion spent running SQL queries (`total_duration`/`sql_duration`). It can help debug N+1 issues and review the impact of configuring eager loading: ```ruby RailsPgExtras.measure_queries { User.limit(10).map(&:team) } # {:count=>11, # :queries=> # {"SELECT \"users\".* FROM \"users\" LIMIT $1"=> # {:count=>1, # :total_duration=>0.003183000022545457, # :min_duration=>0.003183000022545457, # :max_duration=>0.003183000022545457, # :avg_duration=>0.003183000022545457}, # "SELECT \"teams\".* FROM \"teams\" WHERE \"teams\".\"id\" = $1 LIMIT $2"=> # {:count=>10, # :total_duration=>0.011682000011205673, # :min_duration=>0.0007209999894257635, # :max_duration=>0.0024030000204220414, # :avg_duration=>0.0011682000011205673}}, # :total_duration=>0.15247199998702854, # :sql_duration=>0.01486500003375113} RailsPgExtras.measure_queries { User.limit(10).includes(:team).map(&:team) } # {:count=>2, # :queries=> # {"SELECT \"users\".* FROM \"users\" LIMIT $1"=> # {:count=>1, # :total_duration=>0.0036189999955240637, # :min_duration=>0.0036189999955240637, # :max_duration=>0.0036189999955240637, # :avg_duration=>0.0036189999955240637}, # "SELECT \"teams\".* FROM \"teams\" WHERE \"teams\".\"id\" IN ($1, $2, $3, $4, $5, $6, $7, $8)"=> # {:count=>1, # :total_duration=>0.003714999998919666, # :min_duration=>0.003714999998919666, # :max_duration=>0.003714999998919666, # :avg_duration=>0.003714999998919666}}, # :total_duration=>0.023814999993192032, # :sql_duration=>0.0073339999944437295} ``` ### `table_info` This method displays metadata metrics for all or a selected table. You can use it to check the table's size, its cache hit metrics, and whether it is correctly indexed. Many sequential scans or no index scans are potential indicators of misconfigured indexes. This method aggregates data provided by other methods in an easy to analyze summary format. ```ruby RailsPgExtras.table_info(args: { table_name: "users" }) | Table name | Table size | Table cache hit | Indexes cache hit | Estimated rows | Sequential scans | Indexes scans | +------------+------------+-------------------+--------------------+----------------+------------------+---------------+ | users | 2432 kB | 0.999966685701511 | 0.9988780464661853 | 16650 | 2128 | 512496 | ``` ### `index_info` This method returns summary info about database indexes. You can check index size, how often it is used and what percentage of its total size are NULL values. Like the previous method, it aggregates data from other helper methods in an easy-to-digest format. ```ruby RailsPgExtras.index_info(args: { table_name: "users" }) | Index name | Table name | Columns | Index size | Index scans | Null frac | +-------------------------------+------------+----------------+------------+-------------+-----------+ | users_pkey | users | id | 1152 kB | 163007 | 0.00% | | index_users_on_slack_id | users | slack_id | 1080 kB | 258870 | 0.00% | | index_users_on_team_id | users | team_id | 816 kB | 70962 | 0.00% | | index_users_on_uuid | users | uuid | 1032 kB | 0 | 0.00% | | index_users_on_block_uuid | users | block_uuid | 776 kB | 19502 | 100.00% | | index_users_on_api_auth_token | users | api_auth_token | 1744 kB | 156 | 0.00% | ``` ### `cache_hit` ```ruby RailsPgExtras.cache_hit $ rake pg_extras:cache_hit name | ratio ----------------+------------------------ index hit rate | 0.99957765013541945832 table hit rate | 1.00 (2 rows) ``` This command provides information on the efficiency of the buffer cache, for both index reads (`index hit rate`) as well as table reads (`table hit rate`). A low buffer cache hit ratio can be a sign that the Postgres instance is too small for the workload. [More info](https://pawelurbanek.com/postgresql-fix-performance#cache-hit) ### `index_cache_hit` ```ruby RailsPgExtras.index_cache_hit $ rake pg_extras:index_cache_hit | name | buffer_hits | block_reads | total_read | ratio | +-----------------------+-------------+-------------+------------+-------------------+ | teams | 187665 | 109 | 187774 | 0.999419514948821 | | subscriptions | 5160 | 6 | 5166 | 0.99883855981417 | | plans | 5718 | 9 | 5727 | 0.998428496595076 | (truncated results for brevity) ``` The same as `cache_hit` with each table's indexes cache hit info displayed separately. [More info](https://pawelurbanek.com/postgresql-fix-performance#cache-hit) ### `table_cache_hit` ```ruby RailsPgExtras.table_cache_hit $ rake pg_extras:table_cache_hit | name | buffer_hits | block_reads | total_read | ratio | +-----------------------+-------------+-------------+------------+-------------------+ | plans | 32123 | 2 | 32125 | 0.999937743190662 | | subscriptions | 95021 | 8 | 95029 | 0.999915815172211 | | teams | 171637 | 200 | 171837 | 0.99883610631005 | (truncated results for brevity) ``` The same as `cache_hit` with each table's cache hit info displayed seperately. [More info](https://pawelurbanek.com/postgresql-fix-performance#cache-hit) ### `db_settings` ```ruby RailsPgExtras.db_settings $ rake pg_extras:db_settings name | setting | unit | ------------------------------+---------+------+ checkpoint_completion_target | 0.7 | | default_statistics_target | 100 | | effective_cache_size | 1350000 | 8kB | effective_io_concurrency | 1 | | (truncated results for brevity) ``` This method displays values for selected PostgreSQL settings. You can compare them with settings recommended by [PGTune](https://pgtune.leopard.in.ua/#/) and tweak values to improve performance. [More info](https://pawelurbanek.com/postgresql-fix-performance#cache-hit) ### `ssl_used` ```ruby RailsPgExtras.ssl_used | ssl_is_used | +---------------------------------+ | t | ``` Returns boolean indicating if an encrypted SSL is currently used. Connecting to the database via an unencrypted connection is a critical security risk. ### `index_usage` ```ruby RailsPgExtras.index_usage $ rake pg_extras:index_usage relname | percent_of_times_index_used | rows_in_table ---------------------+-----------------------------+--------------- events | 65 | 1217347 app_infos | 74 | 314057 app_infos_user_info | 0 | 198848 user_info | 5 | 94545 delayed_jobs | 27 | 0 (5 rows) ``` This command provides information on the efficiency of indexes, represented as what percentage of total scans were index scans. A low percentage can indicate under indexing, or wrong data being indexed. ### `locks` ```ruby RailsPgExtras.locks(args: { limit: 20 }) $ rake pg_extras:locks procpid | relname | transactionid | granted | query_snippet | mode | age | application | ---------+---------+---------------+---------+-----------------------+------------------------------------------------------ 31776 | | | t | in transaction | ExclusiveLock | 00:19:29.837898 | bin/rails 31776 | | 1294 | t | in transaction | RowExclusiveLock | 00:19:29.837898 | bin/rails 31912 | | | t | select * from hello; | ExclusiveLock | 00:19:17.94259 | bin/rails 3443 | | | t | +| ExclusiveLock | 00:00:00 | bin/sidekiq | | | | select +| | | | | | | pg_stat_activi | | | (4 rows) ``` This command displays queries that have taken out an exclusive lock on a relation. Exclusive locks typically prevent other operations on that relation from taking place, and can be a cause of "hung" queries that are waiting for a lock to be granted. [More info](https://pawelurbanek.com/postgresql-fix-performance#deadlocks) ### `all_locks` ```ruby RailsPgExtras.all_locks $ rake pg_extras:all_locks ``` This command displays all the current locks, regardless of their type. ### `outliers` ```ruby RailsPgExtras.outliers(args: { limit: 20 }) $ rake pg_extras:outliers qry | exec_time | prop_exec_time | ncalls | sync_io_time -----------------------------------------+------------------+----------------+-------------+-------------- SELECT * FROM archivable_usage_events.. | 154:39:26.431466 | 72.2% | 34,211,877 | 00:00:00 COPY public.archivable_usage_events (.. | 50:38:33.198418 | 23.6% | 13 | 13:34:21.00108 COPY public.usage_events (id, reporte.. | 02:32:16.335233 | 1.2% | 13 | 00:34:19.784318 INSERT INTO usage_events (id, retaine.. | 01:42:59.436532 | 0.8% | 12,328,187 | 00:00:00 SELECT * FROM usage_events WHERE (alp.. | 01:18:10.754354 | 0.6% | 102,114,301 | 00:00:00 UPDATE usage_events SET reporter_id =.. | 00:52:35.683254 | 0.4% | 23,786,348 | 00:00:00 (truncated results for brevity) ``` This command displays statements, obtained from `pg_stat_statements`, ordered by the amount of time to execute in aggregate. This includes the statement itself, the total execution time for that statement, the proportion of total execution time for all statements that statement has taken up, the number of times that statement has been called, and the amount of time that statement spent on synchronous I/O (reading/writing from the file system). Typically, an efficient query will have an appropriate ratio of calls to total execution time, with as little time spent on I/O as possible. Queries that have a high total execution time but low call count should be investigated to improve their performance. Queries that have a high proportion of execution time being spent on synchronous I/O should also be investigated. [More info](https://pawelurbanek.com/postgresql-fix-performance#missing-indexes) ### `calls` ```ruby RailsPgExtras.calls(args: { limit: 10 }) $ rake pg_extras:calls qry | exec_time | prop_exec_time | ncalls | sync_io_time -----------------------------------------+------------------+----------------+-------------+-------------- SELECT * FROM usage_events WHERE (alp.. | 01:18:11.073333 | 0.6% | 102,120,780 | 00:00:00 BEGIN | 00:00:51.285988 | 0.0% | 47,288,662 | 00:00:00 COMMIT | 00:00:52.31724 | 0.0% | 47,288,615 | 00:00:00 SELECT * FROM archivable_usage_event.. | 154:39:26.431466 | 72.2% | 34,211,877 | 00:00:00 UPDATE usage_events SET reporter_id =.. | 00:52:35.986167 | 0.4% | 23,788,388 | 00:00:00 (truncated results for brevity) ``` This command is much like `pg:outliers`, but ordered by the number of times a statement has been called. [More info](https://pawelurbanek.com/postgresql-fix-performance#missing-indexes) ### `blocking` ```ruby RailsPgExtras.blocking $ rake pg_extras:blocking blocked_pid | blocking_statement | blocking_duration | blocking_pid | blocked_statement | blocked_duration -------------+--------------------------+-------------------+--------------+------------------------------------------------------------------------------------+------------------ 461 | select count(*) from app | 00:00:03.838314 | 15682 | UPDATE "app" SET "updated_at" = '2013-03-04 15:07:04.746688' WHERE "id" = 12823149 | 00:00:03.821826 (1 row) ``` This command displays statements that are currently holding locks that other statements are waiting to be released. This can be used in conjunction with `pg:locks` to determine which statements need to be terminated in order to resolve lock contention. [More info](https://pawelurbanek.com/postgresql-fix-performance#deadlocks) ### `total_index_size` ```ruby RailsPgExtras.total_index_size $ rake pg_extras:total_index_size size ------- 28194 MB (1 row) ``` This command displays the total size of all indexes on the database, in MB. It is calculated by taking the number of pages (reported in `relpages`) and multiplying it by the page size (8192 bytes). ### `index_size` ```ruby RailsPgExtras.index_size $ rake pg_extras:index_size name | size ---------------------------------------------------------------+--------- idx_activity_attemptable_and_type_lesson_enrollment | 5196 MB index_enrollment_attemptables_by_attempt_and_last_in_group | 4045 MB index_attempts_on_student_id | 2611 MB enrollment_activity_attemptables_pkey | 2513 MB index_attempts_on_student_id_final_attemptable_type | 2466 MB attempts_pkey | 2466 MB index_attempts_on_response_id | 2404 MB index_attempts_on_enrollment_id | 1957 MB index_enrollment_attemptables_by_enrollment_activity_id | 1789 MB enrollment_activities_pkey | 458 MB (truncated results for brevity) ``` This command displays the size of each each index in the database, in MB. It is calculated by taking the number of pages (reported in `relpages`) and multiplying it by the page size (8192 bytes). ### `table_size` ```ruby RailsPgExtras.table_size $ rake pg_extras:table_size name | size ---------------------------------------------------------------+--------- learning_coaches | 196 MB states | 145 MB grade_levels | 111 MB charities_customers | 73 MB charities | 66 MB (truncated results for brevity) ``` This command displays the size of each table and materialized view in the database, in MB. It is calculated by using the system administration function `pg_table_size()`, which includes the size of the main data fork, free space map, visibility map and TOAST data. ### `table_indexes_size` ```ruby RailsPgExtras.table_indexes_size $ rake pg_extras:table_indexes_size table | indexes_size ---------------------------------------------------------------+-------------- learning_coaches | 153 MB states | 125 MB charities_customers | 93 MB charities | 16 MB grade_levels | 11 MB (truncated results for brevity) ``` This command displays the total size of indexes for each table and materialized view, in MB. It is calculated by using the system administration function `pg_indexes_size()`. ### `total_table_size` ```ruby RailsPgExtras.total_table_size $ rake pg_extras:total_table_size name | size ---------------------------------------------------------------+--------- learning_coaches | 349 MB states | 270 MB charities_customers | 166 MB grade_levels | 122 MB charities | 82 MB (truncated results for brevity) ``` This command displays the total size of each table and materialized view in the database, in MB. It is calculated by using the system administration function `pg_total_relation_size()`, which includes table size, total index size and TOAST data. ### `unused_indexes` ```ruby RailsPgExtras.unused_indexes(args: { max_scans: 20 }) $ rake pg_extras:unused_indexes table | index | index_size | index_scans ---------------------+--------------------------------------------+------------+------------- public.grade_levels | index_placement_attempts_on_grade_level_id | 97 MB | 0 public.observations | observations_attrs_grade_resources | 33 MB | 0 public.messages | user_resource_id_idx | 12 MB | 0 (3 rows) ``` This command displays indexes that have < 50 scans recorded against them, and are greater than 5 pages in size, ordered by size relative to the number of index scans. This command is generally useful for eliminating indexes that are unused, which can impact write performance, as well as read performance should they occupy space in memory. [More info](https://pawelurbanek.com/postgresql-fix-performance#unused-indexes) ### `duplicate_indexes` ```ruby RailsPgExtras.duplicate_indexes | size | idx1 | idx2 | idx3 | idx4 | +------------+--------------+----------------+----------+-----------+ | 128 k | users_pkey | index_users_id | | | ``` This command displays multiple indexes that have the same set of columns, same opclass, expression and predicate - which make them equivalent. Usually it's safe to drop one of them. ### `null_indexes` ```ruby RailsPgExtras.null_indexes(args: { min_relation_size_mb: 10 }) $ rake pg_extras:null_indexes oid | index | index_size | unique | indexed_column | null_frac | expected_saving ---------+--------------------+------------+--------+----------------+-----------+----------------- 183764 | users_reset_token | 1445 MB | t | reset_token | 97.00% | 1401 MB 88732 | plan_cancelled_at | 539 MB | f | cancelled_at | 8.30% | 44 MB 9827345 | users_email | 18 MB | t | email | 28.67% | 5160 kB ``` This command displays indexes that contain `NULL` values. A high ratio of `NULL` values means that using a partial index excluding them will be beneficial in case they are not used for searching. [More info](https://pawelurbanek.com/postgresql-fix-performance#null-indexes) ### `seq_scans` ```ruby RailsPgExtras.seq_scans $ rake pg_extras:seq_scans name | count -----------------------------------+---------- learning_coaches | 44820063 states | 36794975 grade_levels | 13972293 charities_customers | 8615277 charities | 4316276 messages | 3922247 contests_customers | 2915972 classroom_goals | 2142014 (truncated results for brevity) ``` This command displays the number of sequential scans recorded against all tables, descending by count of sequential scans. Tables that have very high numbers of sequential scans may be under-indexed, and it may be worth investigating queries that read from these tables. [More info](https://pawelurbanek.com/postgresql-fix-performance#missing-indexes) ### `long_running_queries` ```ruby RailsPgExtras.long_running_queries(args: { threshold: "200 milliseconds" }) $ rake pg_extras:long_running_queries pid | duration | query -------+-----------------+--------------------------------------------------------------------------------------- 19578 | 02:29:11.200129 | EXPLAIN SELECT "students".* FROM "students" WHERE "students"."id" = 1450645 LIMIT 1 19465 | 02:26:05.542653 | EXPLAIN SELECT "students".* FROM "students" WHERE "students"."id" = 1889881 LIMIT 1 19632 | 02:24:46.962818 | EXPLAIN SELECT "students".* FROM "students" WHERE "students"."id" = 1581884 LIMIT 1 (truncated results for brevity) ``` This command displays currently running queries, that have been running for longer than 5 minutes, descending by duration. Very long running queries can be a source of multiple issues, such as preventing DDL statements completing or vacuum being unable to update `relfrozenxid`. ### `records_rank` ```ruby RailsPgExtras.records_rank $ rake pg_extras:records_rank name | estimated_count -----------------------------------+----------------- tastypie_apiaccess | 568891 notifications_event | 381227 core_todo | 178614 core_comment | 123969 notifications_notification | 102101 django_session | 68078 (truncated results for brevity) ``` This command displays an estimated count of rows per table, descending by estimated count. The estimated count is derived from `n_live_tup`, which is updated by vacuum operations. Due to the way `n_live_tup` is populated, sparse vs. dense pages can result in estimations that are significantly out from the real count of rows. ### `bloat` ```ruby RailsPgExtras.bloat $ rake pg_extras:bloat type | schemaname | object_name | bloat | waste -------+------------+-------------------------------+-------+---------- table | public | bloated_table | 1.1 | 98 MB table | public | other_bloated_table | 1.1 | 58 MB index | public | bloated_table::bloated_index | 3.7 | 34 MB table | public | clean_table | 0.2 | 3808 kB table | public | other_clean_table | 0.3 | 1576 kB (truncated results for brevity) ``` This command displays an estimation of table "bloat" – space allocated to a relation that is full of dead tuples, that has yet to be reclaimed. Tables that have a high bloat ratio, typically 10 or greater, should be investigated to see if vacuuming is aggressive enough, and can be a sign of high table churn. [More info](https://pawelurbanek.com/postgresql-fix-performance#bloat) ### `vacuum_stats` ```ruby RailsPgExtras.vacuum_stats $ rake pg_extras:vacuum_stats schema | table | last_vacuum | last_autovacuum | rowcount | dead_rowcount | autovacuum_threshold | expect_autovacuum --------+-----------------------+-------------+------------------+----------------+----------------+----------------------+------------------- public | log_table | | 2013-04-26 17:37 | 18,030 | 0 | 3,656 | public | data_table | | 2013-04-26 13:09 | 79 | 28 | 66 | public | other_table | | 2013-04-26 11:41 | 41 | 47 | 58 | public | queue_table | | 2013-04-26 17:39 | 12 | 8,228 | 52 | yes (truncated results for brevity) ``` This command displays statistics related to vacuum operations for each table, including an estimation of dead rows, last autovacuum and the current autovacuum threshold. This command can be useful when determining if current vacuum thresholds require adjustments, and to determine when the table was last vacuumed. ### `kill_all` ```ruby RailsPgExtras.kill_all ``` This commands kills all the currently active connections to the database. It can be useful as a last resort when your database is stuck in a deadlock. ### `kill_pid` ```ruby RailsPgExtras.kill_pid(args: { pid: 4657 }) ``` This commands kills currently active database connection by its `pid` number. You can use `connections` method to find the correct `pid` values. ### `pg_stat_statements_reset` ```ruby RailsPgExtras.pg_stat_statements_reset ``` This command discards all statistics gathered so far by pg_stat_statements. ### `buffercache_stats` ```ruby RailsPgExtras.buffercache_stats(args: { limit: 10 }) ``` This command shows the relations buffered in database share buffer, ordered by percentage taken. It also shows that how much of the whole relation is buffered. ### `buffercache_usage` ```ruby RailsPgExtras.buffercache_usage(args: { limit: 20 }) ``` This command calculates how many blocks from which table are currently cached. ### `extensions` ```ruby RailsPgExtras.extensions $ rake pg_extras:extensions | pg_stat_statements | 1.7 | 1.7 | track execution statistics of all SQL statements executed (truncated results for brevity) ``` This command lists all the currently installed and available PostgreSQL extensions. ### `connections` ```ruby RailsPgExtras.connections +----------------------------------------------------------------+ | Returns the list of all active database connections | +------------------+--------------------------+------------------+ | username | pid | client_address | application_name | +------------------+--------------------------+------------------+ | postgres | 15962 | 172.31.69.166/32 | sidekiq | | postgres | 16810 | 172.31.69.166/32 | bin/rails | +------------------+--------------------------+------------------+ ``` This command returns the list of all active database connections. ### mandelbrot ```ruby RailsPgExtras.mandelbrot $ rake pg_extras:mandelbrot ``` This command outputs the Mandelbrot set, calculated through SQL. ## Testing ```bash cp docker-compose.yml.sample docker-compose.yml docker compose up -d rake test_all ``` ## Query sources - [https://github.com/heroku/heroku-pg-extras](https://github.com/heroku/heroku-pg-extras) - [https://hakibenita.com/postgresql-unused-index-size](https://hakibenita.com/postgresql-unused-index-size) - [https://sites.google.com/site/itmyshare/database-tips-and-examples/postgres/useful-sqls-to-check-contents-of-postgresql-shared_buffer](https://sites.google.com/site/itmyshare/database-tips-and-examples/postgres/useful-sqls-to-check-contents-of-postgresql-shared_buffer) - [https://wiki.postgresql.org/wiki/Index_Maintenance](https://wiki.postgresql.org/wiki/Index_Maintenance)