The list of all the queries

User-defined routines that use xmin hidden column

Query goal: Find routines that contain a UPDATE or a DELETE statement that search condition refers to the xmin column. If one uses optimistic approach for dealing with the concurrent modifications of data, then xmin values should be presented by views and used in routines that modify or delete rows.
Notes about the query: Refers to the column pg_proc.prokind and thus works starting from PostgreSQL 11. The query does not consider the routines that are a part of an extension. In the returned body of routine the query replaces each newline character with the line break (br) tag for the better readability in case the query result is displayed in a web browser. There could be multiple routines with the same name but with different parameters in the same schema (overloading). Thus, for the unique identification of the routine it is necessary to present also its parameters in addition to the schema name and routine name.
Query type: General (Overview of some aspect of the database.)
Query license: MIT License
Data source: INFORMATION_SCHEMA+system catalog
SQL query: Click on query to copy it

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'
  ELSE 'PROCEDURE' END AS routine_type,
  regexp_replace(pg_get_functiondef(pg_proc.oid),'[\r\n]','<br>','g')  AS routine_src
FROM 
  pg_catalog.pg_proc, 
  pg_catalog.pg_namespace
WHERE 
  pg_proc.pronamespace = pg_namespace.oid 
  AND pg_proc.prokind IN ('f','p') 
  AND pg_get_functiondef(pg_proc.oid)~*'[[:space:]](UPDATE|DELETE)[[:space:]][^;]*[[:space:]]WHERE[[:space:]][^;]*[[:space:]]xmin[[:space:]]*=[[:space:]]*' 
  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 NOT EXISTS (SELECT 1
FROM pg_catalog.pg_depend d 
WHERE EXISTS (SELECT 1 
FROM pg_catalog.pg_extension e 
WHERE d.refobjid=e.oid) 
AND d.objid=pg_proc.oid)
ORDER BY routine_schema, routine_name, parameters;

Collections where the query belongs to

Collection nameCollection description
Find problems by overviewQueries that results point to different aspects of database that might have problems. A human reviewer has to decide based on the results as to whether there are problems or not .

Categories where the query belongs to

Category nameCategory description
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
User-defined routinesQueries of this category provide information about the user-defined routines

Reference materials for further reading

Reference
https://momjian.us/main/blogs/pgblog/2017.html#October_4_2017
https://vladmihalcea.com/a-beginners-guide-to-database-locking-and-the-lost-update-phenomena/
https://www.2ndquadrant.com/en/blog/postgresql-anti-patterns-read-modify-write-cycles/
https://devcenter.heroku.com/articles/postgresql-concurrency

The list of all the queries