Platform Heroku
PG version 13
I have a very busy database and it is reaching near transaction wrap around.
At this point I really want to do the vacuum manually.
My question is that if I do manual vacuuming of individual tables then I can see that the txid restores to its minimum value. But the global txid is not changed.
Is the individual vacuuming of tables enough ?
Do I still have to do vacuum database ?
Yes, a manual VACUUM of individual tables will do the trick.
Look at the relfrozenxid and relminmxid columns in the pg_class entries for that database. Find the oldest ones. One or more of these should be equal to datfrozenxid and datminmxid in pg_database. If you VACUUM those tables, the values for the database should advance.
Related
I have 900+ postgres schemas (which collectively hold 40,000 tables) that I'd like to drop. However, it appears that it wants me to vacuum everything first, because I get this whenever I try to drop a schema.
ERROR: database is not accepting commands to avoid wraparound data loss in database
Is there a way to drop a large number of schemas without having to vacuum first?
IS there any problem is running the vacuum command. It is like a garbage collection for a database. I use postgre database and I use this command before doing any major work like backup or creating a sql scripts of the whole database.
VACUUM reclaims storage occupied by dead tuples. In normal PostgreSQL operation, tuples that are deleted or obsoleted by an update are not physically removed from their table; they remain present until a VACUUM is done. Therefore it's necessary to do VACUUM periodically, especially on frequently-updated tables.
You've got two choices. Do the vacuum, or drop the whole database. xid wrap-around must be avoided.
https://blog.sentry.io/2015/07/23/transaction-id-wraparound-in-postgres
There is not much you can do, except VACUUM oder dropping the database.
In addition, if you don't do the VACUUM, the database will not work for anything, not just for the schemas you want to drop.
We have a postgres database in Amazon RDS. Initially, we needed to load large amount of data quickly, so autovacuum was turned off according to the best practice suggestion from Amazon. Recently I noticed some performance issue when running queries. Then I realized it has not been vacuumed for a long time. As it turns out many tables have lots of dead tuples.
Surprisingly, even after I manually ran vacuum commands on some of the tables, it did not seem to remove these dead tuples at all. vacuum full takes too long to finish which usually ends up timed out after a whole night.
Why does vacuum command not work? What are my other options, restart the instance?
Use VACUUM (VERBOSE) to get detailed statistics of what it is doing and why.
There are three reasons why dead tuples cannot be removed:
There is a long running transaction that has not been closed. You can find the bad boys with
SELECT pid, datname, usename, state, backend_xmin
FROM pg_stat_activity
WHERE backend_xmin IS NOT NULL
ORDER BY age(backend_xmin) DESC;
You can get rid of a transaction with pg_cancel_backend() or pg_terminate_backend().
There are prepared transactions which have not been commited. You can find them with
SELECT gid, prepared, owner, database, transaction
FROM pg_prepared_xacts
ORDER BY age(transaction) DESC;
User COMMIT PREPARED or ROLLBACK PREPARED to close them.
There are replication slots which are not used. Find them with
SELECT slot_name, slot_type, database, xmin
FROM pg_replication_slots
ORDER BY age(xmin) DESC;
Use pg_drop_replication_slot() to delete an unused replication slot.
https://dba.stackexchange.com/a/77587/30035 explains why not all dead tuples are removed.
for vacuum full not to time out, set statement_timeout = 0
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_BestPractices.html#CHAP_BestPractices.PostgreSQL recommends disabling autovacuum for the time of database restore, further they definetely recommend using it:
Important
Not running autovacuum can result in an eventual required outage to
perform a much more intrusive vacuum operation.
Canceling all sessions and vacuuming table should help with previous dead tuples (regarding your suggestion to restart cluster). But what I suggest you to do in first place - switch autovacuum on. And better probably control vacuum on table, not on the whole cluster with autovacuum_vacuum_threshold, (ALTER TABLE) reference here: https://www.postgresql.org/docs/current/static/sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS
We have a postgres database in Amazon RDS. Initially, we needed to load large amount of data quickly, so autovacuum was turned off according to the best practice suggestion from Amazon. Recently I noticed some performance issue when running queries. Then I realized it has not been vacuumed for a long time. As it turns out many tables have lots of dead tuples.
Surprisingly, even after I manually ran vacuum commands on some of the tables, it did not seem to remove these dead tuples at all. vacuum full takes too long to finish which usually ends up timed out after a whole night.
Why does vacuum command not work? What are my other options, restart the instance?
Use VACUUM (VERBOSE) to get detailed statistics of what it is doing and why.
There are three reasons why dead tuples cannot be removed:
There is a long running transaction that has not been closed. You can find the bad boys with
SELECT pid, datname, usename, state, backend_xmin
FROM pg_stat_activity
WHERE backend_xmin IS NOT NULL
ORDER BY age(backend_xmin) DESC;
You can get rid of a transaction with pg_cancel_backend() or pg_terminate_backend().
There are prepared transactions which have not been commited. You can find them with
SELECT gid, prepared, owner, database, transaction
FROM pg_prepared_xacts
ORDER BY age(transaction) DESC;
User COMMIT PREPARED or ROLLBACK PREPARED to close them.
There are replication slots which are not used. Find them with
SELECT slot_name, slot_type, database, xmin
FROM pg_replication_slots
ORDER BY age(xmin) DESC;
Use pg_drop_replication_slot() to delete an unused replication slot.
https://dba.stackexchange.com/a/77587/30035 explains why not all dead tuples are removed.
for vacuum full not to time out, set statement_timeout = 0
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_BestPractices.html#CHAP_BestPractices.PostgreSQL recommends disabling autovacuum for the time of database restore, further they definetely recommend using it:
Important
Not running autovacuum can result in an eventual required outage to
perform a much more intrusive vacuum operation.
Canceling all sessions and vacuuming table should help with previous dead tuples (regarding your suggestion to restart cluster). But what I suggest you to do in first place - switch autovacuum on. And better probably control vacuum on table, not on the whole cluster with autovacuum_vacuum_threshold, (ALTER TABLE) reference here: https://www.postgresql.org/docs/current/static/sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS
We have a postgres database in Amazon RDS. Initially, we needed to load large amount of data quickly, so autovacuum was turned off according to the best practice suggestion from Amazon. Recently I noticed some performance issue when running queries. Then I realized it has not been vacuumed for a long time. As it turns out many tables have lots of dead tuples.
Surprisingly, even after I manually ran vacuum commands on some of the tables, it did not seem to remove these dead tuples at all. vacuum full takes too long to finish which usually ends up timed out after a whole night.
Why does vacuum command not work? What are my other options, restart the instance?
Use VACUUM (VERBOSE) to get detailed statistics of what it is doing and why.
There are three reasons why dead tuples cannot be removed:
There is a long running transaction that has not been closed. You can find the bad boys with
SELECT pid, datname, usename, state, backend_xmin
FROM pg_stat_activity
WHERE backend_xmin IS NOT NULL
ORDER BY age(backend_xmin) DESC;
You can get rid of a transaction with pg_cancel_backend() or pg_terminate_backend().
There are prepared transactions which have not been commited. You can find them with
SELECT gid, prepared, owner, database, transaction
FROM pg_prepared_xacts
ORDER BY age(transaction) DESC;
User COMMIT PREPARED or ROLLBACK PREPARED to close them.
There are replication slots which are not used. Find them with
SELECT slot_name, slot_type, database, xmin
FROM pg_replication_slots
ORDER BY age(xmin) DESC;
Use pg_drop_replication_slot() to delete an unused replication slot.
https://dba.stackexchange.com/a/77587/30035 explains why not all dead tuples are removed.
for vacuum full not to time out, set statement_timeout = 0
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_BestPractices.html#CHAP_BestPractices.PostgreSQL recommends disabling autovacuum for the time of database restore, further they definetely recommend using it:
Important
Not running autovacuum can result in an eventual required outage to
perform a much more intrusive vacuum operation.
Canceling all sessions and vacuuming table should help with previous dead tuples (regarding your suggestion to restart cluster). But what I suggest you to do in first place - switch autovacuum on. And better probably control vacuum on table, not on the whole cluster with autovacuum_vacuum_threshold, (ALTER TABLE) reference here: https://www.postgresql.org/docs/current/static/sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS
I have given a postgres 9.2 DB around 20GB of size.
I looked through the database and saw that it has been never run vacuum and/or analyze on any tables.
Autovacuum is on and the transaction wraparound limit is very far (only 1% of it).
I know nothing about the data activity (number of deletes,inserts, updates), but I see, it uses a lot of index and sequence.
My question is:
does the lack of vacuum and/or analyze affect data integrity (for example a select doesn't show all the rows matches the select from a table or from an index)? The speed of querys and writes doesn't matter.
is it possible that after the vacuum and/or analyze the same query gives a different answer than it would executed before the vacuum/analyze command?
I'm fairly new to PG, thank you for your help!!
Regards,
Figaro88
Running vacuum and/or analyze will not change the result set produced by any select operation (unless there was a bug in PostgreSQL). They may effect the order of results if you do not supply an ORDER BY clause.