Unofficial Python port of ‘s pgextras that provides various statistics for a Postgres instance.
This may be useful when analyzing performance issues. This includes information about locks, index usage, buffer cache hit ratios and vacuum statistics.
python -m pgextras -dsn <DSN> -methods <method-name1> <method-name2> ...
Following <method-name> are valid options.
cache-hit$ python -m pgextras -dsn <DSN> -methods 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 plan is too small for the workload.
index-usage$ python -m pgextras -dsn <DSN> -methods 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$ python -m pgextras -dsn <DSN> -methods locks
procpid | relname | transactionid | granted | query_snippet | age
---------+---------+---------------+---------+-----------------------+-----------------
31776 | | | t | <IDLE> in transaction | 00:19:29.837898
31776 | | 1294 | t | <IDLE> in transaction | 00:19:29.837898
31912 | | | t | select * from hello; | 00:19:17.94259
3443 | | | t | +| 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.
outliers$ python -m pgextras -dsn <DSN> -methods 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
INSERT INTO usage_events (id, retaine.. | 00:49:24.952561 | 0.4% | 21,988,201 | 00:00:00
COPY public.app_ownership_events (id,.. | 00:37:14.31082 | 0.3% | 13 | 00:12:32.584754
INSERT INTO app_ownership_events (id,.. | 00:26:59.808212 | 0.2% | 383,109 | 00:00:00
SELECT * FROM app_ownership_events .. | 00:19:06.021846 | 0.1% | 744,879 | 00:00:00
(10 rows)
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 filesystem).
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.
calls$ python -m pgextras -dsn <DSN> -methods 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
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
SELECT * FROM app_ownership_events .. | 00:19:06.289521 | 0.1% | 744,976 | 00:00:00
INSERT INTO app_ownership_events(id, .. | 00:26:59.885631 | 0.2% | 383,153 | 00:00:00
UPDATE app_ownership_events SET app_i.. | 00:01:22.282337 | 0.0% | 359,741 | 00:00:00
(10 rows)
This command is much like outliers, but ordered by the number of times a statement has been called.
blocking$ python -m pgextras -dsn <DSN> -methods 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 locks to determine which statements need to be terminated in order to resolve lock contention.
total-index-size$ python -m pgextras -dsn <DSN> -methods 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$ python -m pgextras -dsn <DSN> -methods 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
index_enrollment_activities_by_lesson_enrollment_and_activity | 402 MB
index_placement_attempts_on_response_id | 109 MB
index_placement_attempts_on_placement_test_id | 108 MB
index_placement_attempts_on_grade_level_id | 97 MB
index_lesson_enrollments_on_lesson_id | 93 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$ python -m pgextras -dsn <DSN> -methods 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 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$ python -m pgextras -dsn <DSN> -methods 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, in MB. It is calculates by using the system administration function pg_indexes_size().
total-table-size$ python -m pgextras -dsn <DSN> -methods 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 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$ 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.
seq-scans$ python -m pgextras -dsn <DSN> -methods 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
contests | 1370267
goals | 1112659
districts | 158995
rollup_reports | 115942
customers | 93847
schools | 92984
classrooms | 92982
customer_settings | 91226
(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 underindexed, and it may be worth investigating queries that read from these tables.
long-running-queries$ python -m pgextras -dsn <DSN> -methods 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$ python -m pgextras -dsn <DSN> -methods 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$ python -m pgextras -dsn <DSN> -methods 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
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.
vacuum-stats$ python -m pgextras -dsn <DSN> -methods 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
public | picnic_table | | | 13 | 0 | 53 |
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.
user-connections$ python -m pgextras -dsn <DSN> -methods user-connections
Credential Connections
────────────── ───────────
ua7almfsv0d8tq 24
This command displays the number of open connections for each role. This is primarily useful for determining if a specific role is consuming many more connections than expected.
all$ python -m pgextras -dsn <DSN> -methods all
This command displays all above stats at once.