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pawurb
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Description

Ecto PostgreSQL database performance insights. Locks, index usage, buffer cache hit ratios, vacuum stats and more.

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Ecto PSQL Extras Hex.pm Hex.pm Hex.pm CI

Elixir port of Heroku PG Extras. The goal of this project is to provide powerful insights into the PostgreSQL database for Elixir apps that are not using the Heroku PostgreSQL plugin.

Queries 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. Elixir API enables developers to easily integrate the tool into e.g. automatic monitoring tasks.

You can check out this blog post for detailed step by step tutorial on how to optimize PostgreSQL using PG Extras library.

This library is an optional dependency of Phoenix.LiveDashboard. Check it out if you want to see SQL metrics in the UI instead of a command line interface.

Phoenix Ecto Dashboard

Alternative versions:

Installation

mix.exs
 def deps do
    [
      {:ecto_psql_extras, "~> 0.7"}
    ]
 end

Some of the queries (e.g.,

calls
and
outliers
) require pgstatstatements extension enabled.

You can check if it is enabled in your database by running:

EctoPSQLExtras.query(:extensions, YourApp.Repo)

You should see the similar line in the output:

| pg_stat_statements  | 1.7  | 1.7 | track execution statistics of all SQL statements executed |

Usage

You can run queries using a simple API:

EctoPSQLExtras.cache_hit(YourApp.Repo)
+----------------+------------------------+
|        Index and table hit rate         |
+----------------+------------------------+
| name           | ratio                  |
+----------------+------------------------+
| index hit rate | 0.97796610169491525424 |
| table hit rate | 0.96724294813466787989 |
+----------------+------------------------+

By default the ASCII table is displayed. Alternatively you can return the raw query results:

EctoPSQLExtras.index_cache_hit(YourApp.Repo, format: :raw)

%Postgrex.Result{ columns: ["name", "buffer_hits", "block_reads", "total_read", "ratio"], command: :select, connection_id: 413, messages: [], num_rows: 1, rows: [["schema_migrations", 0, 1, 1, "0"]] }

You can also run queries by passing their name to the

query
method:
EctoPSQLExtras.query(:cache_hit, YourApp.Repo)

Some methods accept an optional

args
param allowing you to customize queries:
EctoPSQLExtras.long_running_queries(YourApp.Repo, args: [threshold: "200 milliseconds"])

Available methods

cache_hit

EctoPSQLExtras.cache_hit(YourApp.Repo)

  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

index_cache_hit

EctoPSQLExtras.index_cache_hit(YourApp.Repo)

| 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

table_cache_hit

EctoPSQLExtras.table_cache_hit(YourApp.Repo)

| 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 separately.

More info

db_settings

EctoPSQLExtras.db_settings(YourApp.Repo)

         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 and tweak values to improve performance.

More info

index_usage

EctoPSQLExtras.index_usage(YourApp.Repo)

   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

EctoPSQLExtras.locks(YourApp.Repo)

procpid | relname | transactionid | granted | query_snippet | mode | age ---------+---------+---------------+---------+-----------------------+------------------------------------- 31776 | | | t | in transaction | ExclusiveLock | 00:19:29.837898 31776 | | 1294 | t | in transaction | RowExclusiveLock | 00:19:29.837898 31912 | | | t | select * from hello; | ExclusiveLock | 00:19:17.94259 3443 | | | t | +| ExclusiveLock | 00:00:00 | | | | 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

all_locks

EctoPSQLExtras.all_locks(YourApp.Repo)

This command displays all the current locks, regardless of their type.

outliers

EctoPSQLExtras.outliers(YourApp.Repo, args: [limit: 20])

               query                 |    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 INSERT INTO usage_events (id, retaine.. | 00:49:24.952561 | 0.4% | 21,988,201 | 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

calls

EctoPSQLExtras.calls(YourApp.Repo, args: [limit: 20])

               query                 |    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 INSERT INTO usage_events (id, retaine.. | 00:49:25.260245 | 0.4% | 21,990,326 | 00:00:00 INSERT INTO usage_events (id, retaine.. | 01:42:59.436532 | 0.8% | 12,328,187 | 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

blocking

EctoPSQLExtras.blocking(YourApp.Repo)

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

total_index_size

EctoPSQLExtras.total_index_size(YourApp.Repo)

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

EctoPSQLExtras.index_size(YourApp.Repo)

                         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

EctoPSQLExtras.table_size(YourApp.Repo)

                         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

EctoPSQLExtras.table_indexes_size(YourApp.Repo)

                         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

EctoPSQLExtras.total_table_size(YourApp.Repo)

                         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

EctoPSQLExtras.unused_indexes(YourApp.Repo, args: [min_scans: 20])

      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

duplicate_indexes

EctoPSQLExtras.duplicate_indexes(YourApp.Repo)

| 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

EctoPSQLExtras.null_indexes(YourApp.Repo, args: [min_relation_size_mb: 10])

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 commands 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

seq_scans

EctoPSQLExtras.seq_scans(YourApp.Repo)


           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

long_running_queries

EctoPSQLExtras.long_running_queries(YourApp.Repo, args: [threshold: "200 milliseconds"])


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

EctoPSQLExtras.records_rank(YourApp.Repo)

           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

EctoPSQLExtras.bloat(YourApp.Repo)


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

vacuum_stats

EctoPSQLExtras.vacuum_stats(YourApp.Repo)

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 public | picnic_table | | | 13 | 0 | 53 | (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

EctoPSQLExtras.kill_all(YourApp.Repo)

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.

extensions

EctoPSQLExtras.extensions(YourApp.Repo)

This command lists all the currently installed and available PostgreSQL extensions.

mandelbrot

EctoPSQLExtras.mandelbrot(YourApp.Repo)

This command outputs the Mandelbrot set, calculated through SQL.

Query sources

Development

cp docker-compose.yml.sample docker-compose.yml
docker compose up -d
PG_VERSION=11 mix test --include distribution \
  && PG_VERSION=12 mix test --include distribution \
  && PG_VERSION=13 mix test --include distribution

By default tests will use the following database connection URL compatible with the default

docker-compose.yml
:

ecto://postgres:[email protected]:5432/ecto_psql_extras

Optionally, you can override the following variables:

POSTGRES_USER
POSTGRES_USER
POSTGRES_HOST
POSTGRES_DB

or provide the full

DATABASE_URL
connection URL.

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