Excessive locking with FOR UPDATE in subqueries

Back to Catalog
Goal This query identifies performance and concurrency bottlenecks caused by excessive locking. It flags INSERT, UPDATE, or DELETE statements that utilize subqueries containing the FOR UPDATE clause. Using FOR UPDATE acquires an exclusive lock, which is semantically inappropriate if the rows in the subquery are merely being read for reference or validation rather than being modified. This practice degrades system concurrency by unnecessarily blocking other transactions.
Notes A subquery can be in the WHERE clause or in a common table expression (WITH clause).
Type Problem detection (Each row in the result could represent a flaw in the design)
Reliability Medium (Medium number of false-positive results)
License MIT License
Fixing Suggestion A weaker lock mode, such as FOR SHARE, is generally sufficient to ensure referential integrity without preventing concurrent reads.
Data Source INFORMATION_SCHEMA+system catalog
SQL Query 
SELECT 
  pg_namespace.nspname AS routine_schema, 
  pg_proc.proname AS routine_name, 
  pg_get_function_identity_arguments(pg_proc.oid) AS parameters,
  CASE WHEN pg_proc.prokind='f' THEN 'FUNCTION'
  WHEN pg_proc.prokind='p' THEN 'PROCEDURE'
  WHEN pg_proc.prokind='w' THEN 'WINDOW FUNCTION' END AS routine_type,
   regexp_replace( regexp_replace(pg_get_functiondef(pg_proc.oid),'<','<','g'),'[\r\n]','
','g')  AS routine_src
FROM 
  pg_catalog.pg_proc, 
  pg_catalog.pg_namespace
WHERE 
  pg_proc.pronamespace = pg_namespace.oid
  AND pg_proc.prokind<>'a'
 AND pg_proc.proname NOT IN ('f_assume_you_must_use_files', 'f_check_format_comma_separated_list', 'f_check_password', 'f_default_value_with_no_match') 
 AND pg_namespace.nspname NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL) 
AND (pg_get_functiondef(pg_proc.oid)~*'(INSERT|UPDATE|DELETE)[[:space:]]+[^;]+[(][[:space:]]*SELECT(?=[^;]+FOR[[:space:]]+UPDATE)'
OR pg_get_functiondef(pg_proc.oid)~*'WITH[^;]+SELECT[^;]+FOR[[:space:]]+UPDATE[^;]+(INSERT|UPDATE|DELETE)[[:space:]]')
AND pg_get_functiondef(pg_proc.oid)!~'xmin'
ORDER BY routine_schema, routine_name, parameters;
Collections

This query belongs to the following collections:

NameDescription
Find problems automaticallyQueries, that results point to problems in the database. Each query in the collection produces an initial assessment. However, a human reviewer has the final say as to whether there is a problem or not .
Categories

This query is classified under the following categories:

NameDescription
Concurrency controlQueries of this category provide information about concurrency control.
Does not work in some earlier PostgreSQL versionQueries of this category provide information that was not available in some earlier PostgreSQL version
TransactionsQueries of this catergory provide information about the use of transactions.
User-defined routinesQueries of this category provide information about the user-defined routines