pg_tables lock duration in postgresql - postgresql

Question

When we run a query like create table in postgresql,the dictionary table pg_tables gets locked for a certain duration.Is there any command or query using which we can track out for how long any query locks the dictionary table?
I have accessed pg_locks table but it only shows the type of lock.I need to find the duration for which the pg_tables is locked by an executing query.

Answer 1

Postgres has not any tool for lock time monitoring. We had a patch to Postgres for this purpose. Anyway - the pg_tables is not the table - it is view
postgres=# \d+ pg_tables;
View "pg_catalog.pg_tables"
+-------------+---------+-----------+----------+---------+---------+-------------+
| Column | Type | Collation | Nullable | Default | Storage | Description |
+-------------+---------+-----------+----------+---------+---------+-------------+
| schemaname | name | | | | plain | |
| tablename | name | | | | plain | |
| tableowner | name | | | | plain | |
| tablespace | name | | | | plain | |
| hasindexes | boolean | | | | plain | |
| hasrules | boolean | | | | plain | |
| hastriggers | boolean | | | | plain | |
| rowsecurity | boolean | | | | plain | |
+-------------+---------+-----------+----------+---------+---------+-------------+
View definition:
SELECT n.nspname AS schemaname,
c.relname AS tablename,
pg_get_userbyid(c.relowner) AS tableowner,
t.spcname AS tablespace,
c.relhasindex AS hasindexes,
c.relhasrules AS hasrules,
c.relhastriggers AS hastriggers,
c.relrowsecurity AS rowsecurity
FROM pg_class c
LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
LEFT JOIN pg_tablespace t ON tpostgres=# \d+ pg_tables;
View "pg_catalog.pg_tables"
+-------------+---------+-----------+----------+---------+---------+-------------+
| Column | Type | Collation | Nullable | Default | Storage | Description |
+-------------+---------+-----------+----------+---------+---------+-------------+
| schemaname | name | | | | plain | |
| tablename | name | | | | plain | |
| tableowner | name | | | | plain | |
| tablespace | name | | | | plain | |
| hasindexes | boolean | | | | plain | |
| hasrules | boolean | | | | plain | |
| hastriggers | boolean | | | | plain | |
| rowsecurity | boolean | | | | plain | |
+-------------+---------+-----------+----------+---------+---------+-------------+
View definition:
SELECT n.nspname AS schemaname,
c.relname AS tablename,
pg_get_userbyid(c.relowner) AS tableowner,
t.spcname AS tablespace,
c.relhasindex AS hasindexes,
c.relhasrules AS hasrules,
c.relhastriggers AS hastriggers,
c.relrowsecurity AS rowsecurity
FROM pg_class c
LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
LEFT JOIN pg_tablespace t ON t.oid = c.reltablespace
WHERE c.relkind = ANY (ARRAY['r'::"char", 'p'::"char"]);
.oid = c.reltablespace
WHERE c.relkind = ANY (ARRAY['r'::"char", 'p'::"char"]);
You can check if one or more from these tables are not locked - there should be only few operations that can lock these tables against reading. More documentation about it https://wiki.postgresql.org/wiki/Lock_Monitoring