Postgresql Useful SQL/Commands

Posted 2021-11-29 tben

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Show Running Sqls

-- show running queries (pre 9.2)
SELECT procpid, age(clock_timestamp(), query_start), usename, current_query 
FROM pg_stat_activity 
WHERE current_query != ‘<IDLE>‘ AND current_query NOT ILIKE ‘%pg_stat_activity%‘ 
ORDER BY query_start desc;

-- show running queries (9.2)
SELECT pid, age(clock_timestamp(), query_start), usename, query 
FROM pg_stat_activity 
WHERE query != ‘<IDLE>‘ AND query NOT ILIKE ‘%pg_stat_activity%‘ 
ORDER BY query_start desc;

-- show running sqls more than 2 mins (9.2+)
SELECT now() - query_start as "runtime", usename, datname,  state, query
  FROM  pg_stat_activity
  WHERE now() - query_start > ‘2 minutes‘::interval
 ORDER BY runtime DESC;

--show all queries 
select substr(query,1,100) query,backend_type,application_name,query_start,wait_event_type,wait_event,state from pg_stat_activity;

Vacuum

--get vacuum status and results
select relname,last_vacuum, last_autovacuum, last_analyze, last_autoanalyze from pg_stat_user_tables;

--query by sigle table of vacuum status
select relname, n_dead_tup, last_vacuum, last_autovacuum from pg_catalog.pg_stat_all_tables where n_dead_tup > 0 and relname =‘sxacc-devices‘ order by n_dead_tup desc;

-- vacuum command 
VACUUM (VERBOSE, ANALYZE);

Database and Tables releated

-- table index usage rates (should not be less than 0.99)
SELECT relname, 
  CASE WHEN (seq_scan + idx_scan) != 0
    THEN 100.0 * idx_scan / (seq_scan + idx_scan) 
    ELSE 0
  END AS percent_of_times_index_used,
  n_live_tup AS rows_in_table
FROM pg_stat_user_tables 
ORDER BY n_live_tup DESC;

-- all database users 
select * from pg_stat_activity where current_query not like ‘<%‘; 

-- all databases and their sizes 
select * from pg_user; 

-- all tables and their size, with/without indexes 
select datname, pg_size_pretty(pg_database_size(datname)) from pg_database order by pg_database_size(datname) desc; 

-- cache hit rates (should not be less than 0.99) 
SELECT sum(heap_blks_read) as heap_read, sum(heap_blks_hit) as heap_hit, (sum(heap_blks_hit) - sum(heap_blks_read)) / sum(heap_blks_hit) as ratio FROM pg_statio_user_tables; 

-- table index usage rates (should not be less than 0.99) 
SELECT relname, 100 * idx_scan / (seq_scan + idx_scan) percent_of_times_index_used, n_live_tup rows_in_table FROM pg_stat_user_tables ORDER BY n_live_tup DESC; 

-- how many indexes are in cache 
SELECT sum(idx_blks_read) as idx_read, sum(idx_blks_hit) as idx_hit, (sum(idx_blks_hit) - sum(idx_blks_read)) / sum(idx_blks_hit) as ratio FROM pg_statio_user_indexes; 

-- check the size(as in disk space) of all databases;

SELECT d.datname AS Name, pg_catalog.pg_get_userbyid(d.datdba) AS Owner,
  CASE WHEN pg_catalog.has_database_privilege(d.datname, ‘CONNECT‘)
    THEN pg_catalog.pg_size_pretty(pg_catalog.pg_database_size(d.datname)) 
    ELSE ‘No Access‘ 
  END AS SIZE 
FROM pg_catalog.pg_database d 
ORDER BY 
  CASE WHEN pg_catalog.has_database_privilege(d.datname, ‘CONNECT‘) 
    THEN pg_catalog.pg_database_size(d.datname)
    ELSE NULL 
  END;

--check the size(as in space) of each table

SELECT nspname || ‘.‘ || relname AS "relation",
   pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"
 FROM pg_class C
 LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
 WHERE nspname NOT IN (‘pg_catalog‘, ‘information_schema‘)
   AND C.relkind <> ‘i‘
   AND nspname !~ ‘^pg_toast‘
 ORDER BY pg_total_relation_size(C.oid) DESC;

-- all tables and their size, with/without indexes
select datname, pg_size_pretty(pg_database_size(datname))
from pg_database
order by pg_database_size(datname) desc;

-- show unused indexes:

SELECT relname AS table_name, indexrelname AS index_name, idx_scan, idx_tup_read, idx_tup_fetch, pg_size_pretty(pg_relation_size(indexrelname::regclass))
FROM pg_stat_all_indexes
WHERE schemaname = ‘public‘
AND idx_scan = 0
AND idx_tup_read = 0
AND idx_tup_fetch = 0
ORDER BY pg_relation_size(indexrelname::regclass) DESC;

locks

-- all locks
SELECT t.relname, l.locktype, page, virtualtransaction, pid, mode, granted 
FROM pg_locks l, pg_stat_all_tables t 
WHERE l.relation = t.relid ORDER BY relation asc;

-- Сombination of blocked and blocking activity 
-- The following query may be helpful to see what processes are blocking SQL statements (these only find row-level locks, not object-level locks).
SELECT blocked_locks.pid     AS blocked_pid,
         blocked_activity.usename  AS blocked_user,
         blocking_locks.pid     AS blocking_pid,
         blocking_activity.usename AS blocking_user,
         blocked_activity.query    AS blocked_statement,
         blocking_activity.query   AS current_statement_in_blocking_process
   FROM  pg_catalog.pg_locks         blocked_locks
    JOIN pg_catalog.pg_stat_activity blocked_activity  ON blocked_activity.pid = blocked_locks.pid
    JOIN pg_catalog.pg_locks         blocking_locks 
        ON blocking_locks.locktype = blocked_locks.locktype
        AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE
        AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
        AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
        AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
        AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
        AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
        AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
        AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
        AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
        AND blocking_locks.pid != blocked_locks.pid
 
    JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
   WHERE NOT blocked_locks.GRANTED;


--  Here‘s an alternate view of that same data that includes application_name‘s

-- Setting application_name variable in the begging of each transaction allows you to which logical process blocks another one. It can be information which source code line starts transaction or any other information that helps you to match application_name to your code. 
SET application_name=‘%your_logical_name%‘;

SELECT blocked_locks.pid     AS blocked_pid,
         blocked_activity.usename  AS blocked_user,
         blocking_locks.pid     AS blocking_pid,
         blocking_activity.usename AS blocking_user,
         blocked_activity.query    AS blocked_statement,
         blocking_activity.query   AS current_statement_in_blocking_process,
         blocked_activity.application_name AS blocked_application,
         blocking_activity.application_name AS blocking_application
   FROM  pg_catalog.pg_locks         blocked_locks
    JOIN pg_catalog.pg_stat_activity blocked_activity  ON blocked_activity.pid = blocked_locks.pid
    JOIN pg_catalog.pg_locks         blocking_locks 
        ON blocking_locks.locktype = blocked_locks.locktype
        AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE
        AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
        AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
        AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
        AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
        AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
        AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
        AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
        AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
        AND blocking_locks.pid != blocked_locks.pid
 
    JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
   WHERE NOT blocked_locks.GRANTED;


-- Here‘s an alternate view of that same data that includes an idea how old the state is 
SELECT a.datname,
         l.relation::regclass,
         l.transactionid,
         l.mode,
         l.GRANTED,
         a.usename,
         a.query,
         a.query_start,
         age(now(), a.query_start) AS "age",
         a.pid
FROM pg_stat_activity a
JOIN pg_locks l ON l.pid = a.pid
ORDER BY a.query_start;



-- Flat view of Blocking
-- For PostgreSQL Version < 9.2
SELECT 
    waiting.locktype           AS waiting_locktype,
    waiting.relation::regclass AS waiting_table,
    waiting_stm.current_query  AS waiting_query,
    waiting.mode               AS waiting_mode,
    waiting.pid                AS waiting_pid,
    other.locktype             AS other_locktype,
    other.relation::regclass   AS other_table,
    other_stm.current_query    AS other_query,
    other.mode                 AS other_mode,
    other.pid                  AS other_pid,
    other.GRANTED              AS other_granted
FROM
    pg_catalog.pg_locks AS waiting
JOIN
    pg_catalog.pg_stat_activity AS waiting_stm
    ON (
        waiting_stm.procpid = waiting.pid
    )
JOIN
    pg_catalog.pg_locks AS other
    ON (
        (
            waiting."database" = other."database"
        AND waiting.relation  = other.relation
        )
        OR waiting.transactionid = other.transactionid
    )
JOIN
    pg_catalog.pg_stat_activity AS other_stm
    ON (
        other_stm.procpid = other.pid
    )
WHERE
    NOT waiting.GRANTED
AND
    waiting.pid <> other.pid


-- For PostgreSQL Version >= 9.2
SELECT 
    waiting.locktype           AS waiting_locktype,
    waiting.relation::regclass AS waiting_table,
    waiting_stm.query          AS waiting_query,
    waiting.mode               AS waiting_mode,
    waiting.pid                AS waiting_pid,
    other.locktype             AS other_locktype,
    other.relation::regclass   AS other_table,
    other_stm.query            AS other_query,
    other.mode                 AS other_mode,
    other.pid                  AS other_pid,
    other.GRANTED              AS other_granted
FROM
    pg_catalog.pg_locks AS waiting
JOIN
    pg_catalog.pg_stat_activity AS waiting_stm
    ON (
        waiting_stm.pid = waiting.pid
    )
JOIN
    pg_catalog.pg_locks AS other
    ON (
        (
            waiting."database" = other."database"
        AND waiting.relation  = other.relation
        )
        OR waiting.transactionid = other.transactionid
    )
JOIN
    pg_catalog.pg_stat_activity AS other_stm
    ON (
        other_stm.pid = other.pid
    )
WHERE
    NOT waiting.GRANTED
AND
    waiting.pid <> other.pid



-- Recursive View of Blocking
WITH RECURSIVE
     c(requested, CURRENT) AS
       ( VALUES
         (‘AccessShareLock‘::text, ‘AccessExclusiveLock‘::text),
         (‘RowShareLock‘::text, ‘ExclusiveLock‘::text),
         (‘RowShareLock‘::text, ‘AccessExclusiveLock‘::text),
         (‘RowExclusiveLock‘::text, ‘ShareLock‘::text),
         (‘RowExclusiveLock‘::text, ‘ShareRowExclusiveLock‘::text),
         (‘RowExclusiveLock‘::text, ‘ExclusiveLock‘::text),
         (‘RowExclusiveLock‘::text, ‘AccessExclusiveLock‘::text),
         (‘ShareUpdateExclusiveLock‘::text, ‘ShareUpdateExclusiveLock‘::text),
         (‘ShareUpdateExclusiveLock‘::text, ‘ShareLock‘::text),
         (‘ShareUpdateExclusiveLock‘::text, ‘ShareRowExclusiveLock‘::text),
         (‘ShareUpdateExclusiveLock‘::text, ‘ExclusiveLock‘::text),
         (‘ShareUpdateExclusiveLock‘::text, ‘AccessExclusiveLock‘::text),
         (‘ShareLock‘::text, ‘RowExclusiveLock‘::text),
         (‘ShareLock‘::text, ‘ShareUpdateExclusiveLock‘::text),
         (‘ShareLock‘::text, ‘ShareRowExclusiveLock‘::text),
         (‘ShareLock‘::text, ‘ExclusiveLock‘::text),
         (‘ShareLock‘::text, ‘AccessExclusiveLock‘::text),
         (‘ShareRowExclusiveLock‘::text, ‘RowExclusiveLock‘::text),
         (‘ShareRowExclusiveLock‘::text, ‘ShareUpdateExclusiveLock‘::text),
         (‘ShareRowExclusiveLock‘::text, ‘ShareLock‘::text),
         (‘ShareRowExclusiveLock‘::text, ‘ShareRowExclusiveLock‘::text),
         (‘ShareRowExclusiveLock‘::text, ‘ExclusiveLock‘::text),
         (‘ShareRowExclusiveLock‘::text, ‘AccessExclusiveLock‘::text),
         (‘ExclusiveLock‘::text, ‘RowShareLock‘::text),
         (‘ExclusiveLock‘::text, ‘RowExclusiveLock‘::text),
         (‘ExclusiveLock‘::text, ‘ShareUpdateExclusiveLock‘::text),
         (‘ExclusiveLock‘::text, ‘ShareLock‘::text),
         (‘ExclusiveLock‘::text, ‘ShareRowExclusiveLock‘::text),
         (‘ExclusiveLock‘::text, ‘ExclusiveLock‘::text),
         (‘ExclusiveLock‘::text, ‘AccessExclusiveLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘AccessShareLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘RowShareLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘RowExclusiveLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘ShareUpdateExclusiveLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘ShareLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘ShareRowExclusiveLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘ExclusiveLock‘::text),
         (‘AccessExclusiveLock‘::text, ‘AccessExclusiveLock‘::text)
       ),
     l AS
       (
         SELECT
             (locktype,DATABASE,relation::regclass::text,page,tuple,virtualxid,transactionid,classid,objid,objsubid) AS target,
             virtualtransaction,
             pid,
             mode,
             GRANTED
           FROM pg_catalog.pg_locks
       ),
     t AS
       (
         SELECT
             blocker.target  AS blocker_target,
             blocker.pid     AS blocker_pid,
             blocker.mode    AS blocker_mode,
             blocked.target  AS target,
             blocked.pid     AS pid,
             blocked.mode    AS mode
           FROM l blocker
           JOIN l blocked
             ON ( NOT blocked.GRANTED
              AND blocker.GRANTED
              AND blocked.pid != blocker.pid
              AND blocked.target IS NOT DISTINCT FROM blocker.target)
           JOIN c ON (c.requested = blocked.mode AND c.CURRENT = blocker.mode)
       ),
     r AS
       (
         SELECT
             blocker_target,
             blocker_pid,
             blocker_mode,
             ‘1‘::INT        AS depth,
             target,
             pid,
             mode,
             blocker_pid::text || ‘,‘ || pid::text AS seq
           FROM t
         UNION ALL
         SELECT
             blocker.blocker_target,
             blocker.blocker_pid,
             blocker.blocker_mode,
             blocker.depth + 1,
             blocked.target,
             blocked.pid,
             blocked.mode,
             blocker.seq || ‘,‘ || blocked.pid::text
           FROM r blocker
           JOIN t blocked
             ON (blocked.blocker_pid = blocker.pid)
           WHERE blocker.depth < 1000
       )
SELECT * FROM r
  ORDER BY seq;

-- the following view also adds useful information about the sessions in the blocking tree. 
CREATE OR REPLACE VIEW blocking_tree AS
WITH RECURSIVE
  LOCK AS (
  SELECT pid,
     virtualtransaction,
     GRANTED,
     mode,
    (locktype,
     CASE locktype
       WHEN ‘relation‘      THEN concat_ws(‘;‘, ‘db:‘||datname, ‘rel:‘||relation::regclass::text)
       WHEN ‘extend‘        THEN concat_ws(‘;‘, ‘db:‘||datname, ‘rel:‘||relation::regclass::text)
       WHEN ‘page‘          THEN concat_ws(‘;‘, ‘db:‘||datname, ‘rel:‘||relation::regclass::text, ‘page#‘||page::text)
       WHEN ‘tuple‘         THEN concat_ws(‘;‘, ‘db:‘||datname, ‘rel:‘||relation::regclass::text, ‘page#‘||page::text, ‘tuple#‘||tuple::text)
       WHEN ‘transactionid‘ THEN transactionid::text
       WHEN ‘virtualxid‘    THEN virtualxid::text
       WHEN ‘object‘        THEN concat_ws(‘;‘, ‘class:‘||classid::regclass::text, ‘objid:‘||objid, ‘col#‘||objsubid)
       ELSE concat(‘db:‘||datname) -- userlock and advisory
     END::text) AS target
  FROM pg_catalog.pg_locks
  LEFT JOIN pg_catalog.pg_database ON (pg_database.oid = pg_locks.DATABASE)
  )
, waiting_lock AS (
  SELECT
    blocker.pid                         AS blocker_pid,
    blocked.pid                         AS pid,
    concat(blocked.mode,blocked.target) AS lock_target
  FROM LOCK blocker
  JOIN LOCK blocked
    ON ( NOT blocked.GRANTED
     AND blocker.GRANTED
     AND blocked.pid != blocker.pid
     AND blocked.target IS NOT DISTINCT FROM blocker.target)
  JOIN lock_composite c ON (c.requested = blocked.mode AND c.CURRENT = blocker.mode)
  )
, acquired_lock AS (
  WITH waiting AS (
    SELECT lock_target, COUNT(lock_target) AS wait_count FROM waiting_lock GROUP BY lock_target
  )
  SELECT
    pid,
    array_agg(concat(mode,target,‘ + ‘||wait_count) ORDER BY wait_count DESC NULLS LAST) AS locks_acquired
  FROM LOCK
    LEFT JOIN waiting ON waiting.lock_target = concat(mode,target)
  WHERE GRANTED
  GROUP BY pid
  )
, blocking_lock AS (
  SELECT
    ARRAY[date_part(‘epoch‘, query_start)::INT, pid] AS seq,
     0::INT AS depth,
    -1::INT AS blocker_pid,
    pid,
    concat(‘Connect: ‘,usename,‘ ‘,datname,‘ ‘,COALESCE(host(client_addr)||‘:‘||client_port, ‘local‘)
      , E‘\nSQL: ‘,REPLACE(substr(COALESCE(query,‘N/A‘), 1, 60), E‘\n‘, ‘ ‘)
      , E‘\nAcquired:\n  ‘
      , array_to_string(locks_acquired[1:5] ||
                        CASE WHEN array_upper(locks_acquired,1) > 5
                             THEN ‘... ‘||(array_upper(locks_acquired,1) - 5)::text||‘ more ...‘
                        END,
                        E‘\n  ‘)
    ) AS lock_info,
    concat(to_char(query_start, CASE WHEN age(query_start) > ‘24h‘ THEN ‘Day DD Mon‘ ELSE ‘HH24:MI:SS‘ END),E‘ started\n‘
          ,CASE WHEN waiting THEN ‘waiting‘ ELSE state END,E‘\n‘
          ,date_trunc(‘second‘,age(now(),query_start)),‘ ago‘
    ) AS lock_state
  FROM acquired_lock blocker
  LEFT JOIN pg_stat_activity act USING (pid)
  WHERE EXISTS     -- The root of the tree should blocks one or more sessions.
         (SELECT ‘x‘ FROM waiting_lock blocked WHERE blocked.blocker_pid = blocker.pid)
    AND NOT EXISTS -- The root of the tree should not be a blocked session.
         (SELECT ‘x‘ FROM waiting_lock blocked WHERE blocked.pid = blocker.pid)
UNION ALL
  SELECT
    blocker.seq || blocked.pid,
    blocker.depth + 1,
    blocker.pid,
    blocked.pid,
    concat(‘Connect: ‘,usename,‘ ‘,datname,‘ ‘,COALESCE(host(client_addr)||‘:‘||client_port, ‘local‘)
      , E‘\nSQL: ‘,REPLACE(substr(COALESCE(query,‘N/A‘), 1, 60), E‘\n‘, ‘ ‘)
      , E‘\nWaiting: ‘,blocked.lock_target
      , CASE WHEN locks_acquired IS NOT NULL
             THEN E‘\nAcquired:\n  ‘ ||
                  array_to_string(locks_acquired[1:5] ||
                                  CASE WHEN array_upper(locks_acquired,1) > 5
                                       THEN ‘... ‘||(array_upper(locks_acquired,1) - 5)::text||‘ more ...‘
                                  END,
                                  E‘\n  ‘)
        END
    ) AS lock_info,
    concat(to_char(query_start, CASE WHEN age(query_start) > ‘24h‘ THEN ‘Day DD Mon‘ ELSE ‘HH24:MI:SS‘ END),E‘ started\n‘
          ,CASE WHEN waiting THEN ‘waiting‘ ELSE state END,E‘\n‘
          ,date_trunc(‘second‘,age(now(),query_start)),‘ ago‘
    ) AS lock_state
  FROM blocking_lock blocker
  JOIN waiting_lock blocked
    ON (blocked.blocker_pid = blocker.pid)
  LEFT JOIN pg_stat_activity act ON (act.pid = blocked.pid)
  LEFT JOIN acquired_lock acq ON (acq.pid = blocked.pid)
  WHERE blocker.depth < 5
  )
SELECT concat(lpad(‘=> ‘, 4*depth, ‘ ‘),pid::text) AS "PID"
, lock_info AS "Lock Info"
, lock_state AS "State"
FROM blocking_lock
ORDER BY seq;

Other Operations

-- Dump database on remote host to file
$ pg_dump -U username -h hostname databasename > dump.sql

-- Import dump into existing database
$ psql -d newdb -f dump.sql

-- kill running query
SELECT pg_cancel_backend(procpid);

-- kill idle query
SELECT pg_terminate_backend(procpid);

postgres upgrading

# Taken from http://robots.thoughtbot.com/post/33706558963/migrating-data-from-an-upgraded-postgres
#
# Note: these steps assume installation with Homebrew.

# Initialize a new database, adding a .new suffix to the directory that Homebrew recommends.

initdb /usr/local/var/postgres.new -E utf8

# Run the upgrade script, providing the correct paths for the various flags.

pg_upgrade   -b /usr/local/Cellar/postgresql/9.1.4/bin   -B /usr/local/Cellar/postgresql/9.2.1/bin   -d /usr/local/var/postgres   -D /usr/local/var/postgres.new

# Put the data in the correct place.

rm -rf /usr/local/var/postgres
mv /usr/local/var/postgres.new /usr/local/var/postgres

# If you’ve set up launchd to run Postgres automatically, 
# everything should be up and running! Otherwise, check out the 
# documentation with brew info postgres to read how to have OS X 
# manage postgres for you.


#######

# Alternatively, if you’ve just upgraded Postgres with Homebrew and 
# Postgres won’t start, as long as you don’t care about any data stored locally:

brew remove --force postgresql
rm -rf /usr/local/var/postgres/ 
brew install postgresql

postgresql configuration optimization

Memory
Only four values really matter:
    shared-buffers: below 2GB: set it to 20% of full memory; below 32GB: 25% of your full memory.
    work_mem: Start low at 32/64MB. Look for temporary file lines in logs. Then set it to 2-3x the largest temp file that you see. This setting can give a huge speed boost (if set properly).
    maintenance_work_mem: Set it to 10% of system memory.
    effective_cache_size: Only a hint to postgres. Just set it to the amount of filesystem cache available.

Reference:

https://gist.github.com/rgreenjr/3637525
https://wiki.postgresql.org/wiki/Lock_dependency_information
https://wiki.postgresql.org/wiki/Lock_Monitoring

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