Re: is it safe to drop 25 tb schema with cascade option? - Mailing list pgsql-general

On 9/19/19 1:30 PM, Julie Nishimura wrote:
> Adrian, thanks for your reply. We do run VACUUM on pg_catalog every day
> (while the system is online). Should I try to run VACUUM FULL on
> pg_catalog? is it the same as you referring system catalogs?

I would avoid VACUUM FULL as it acquires an exclusive lock on the table
and rewrites the table.:

https://www.postgresql.org/docs/8.2/sql-vacuum.html

A VACUUM w/o FULL will make space available for new tuples which is what
you want.

>
> Thank you!
>
> ------------------------------------------------------------------------
> *From:* Adrian Klaver <adrian.klaver@aklaver.com>
> *Sent:* Thursday, September 19, 2019 12:38 PM
> *To:* Julie Nishimura <juliezain@hotmail.com>; t
> pgsql-general@lists.postgresql.org <pgsql-general@lists.postgresql.org>;
> pgsql-general <pgsql-general@postgresql.org>
> *Subject:* Re: is it safe to drop 25 tb schema with cascade option?
> On 9/19/19 12:06 PM, Julie Nishimura wrote:
>> Hello, we've recently inherited large Greenplum system (master with
>> standby and 8 segment nodes), which is running old version of GP:
>>
>> 20190919:15:22:01:122002 gpstate:hitw-mck-gp1-mdw-1:gpadmin-[INFO]:-  
>> Greenplum initsystem version   = 4.3.4.0 build 1
>> 20190919:15:22:01:122002 gpstate:hitw-mck-gp1-mdw-1:gpadmin-[INFO]:-  
>> Greenplum current version      = PostgreSQL 8.2.15 (Greenplum
>>   Database 4.3.8.1 build 1) on x86_64-unknown-linux-gnu, compiled by GCC
>> gcc (GCC) 4.4.2 compiled on Apr 20 2016 08:08:56
>> 20190919:15:22:01:122002 gpstate:hitw-mck-gp1-mdw-1:gpadmin-[INFO]:-  
>> Postgres version               = 8.2.15
>>
>> If I scan logs, for the last 6 months I see the following warning after
>> every transaction:
>> 04 UTC,0,con9059926,cmd1,seg-1,,,,sx1,"WARNING","01000","database
>> ""my_db_name"" must be vacuumed within 1607900488 transactions",,"To
>> avoid a database shutdown, execute a full-database VACUUM in
>> ""my_db_name"".",,,,"set client_encoding to 'SQL_ASCII'",0,,"varsup.c",109,
>>
>> The database "my_db_name" is 32 TB. According to the crontab logs, we
>> run VACUUM on pg_catalog every day (while the system is online). Should
>> I try to run VACUUM FULL on pg_catalog first, or I need to run VACUUM on
>> the entire "my_db_name"? I am not sure what I should try first.
>
> The vacuum warning is about transaction id wrap around:
>
> https://www.postgresql.org/docs/8.2/routine-vacuuming.html#VACUUM-FOR-WRAPAROUND
>
> You will need to vacuum more then just pg_catalog. You will need to do
> what the message says, vacuum the entire database.
>
>>
>> For the full picture: the largest schema on "my_db_name" was "temp", it
>> was consuming about 25 tb. So what we did - we renamed this schema to
>> "temp_orig", and created brand new schema "temp" (to make drop objects
>> from temp_orig easier and isolated). However, I was hesitating to drop
>> the entire schema that big in one transaction, and started dropping
>> tables from "temp_orig", however, there are millions of objects in that
>> schema, and as a result, number of "drop table" transactions are very
>> high. How safe is it to run "DROPSCHEMAtemp_orig CASCADE" if the schema
>> is almost 25 tb?
>
> Not sure.
>
>>
>> We are running out of space very quickly. we have only 5% left on a device
>>
>> Last time when we dropped millions of objects from that old schema, we
>> were able to free up some space, but this time around even though I am
>> running a lot of "drop tables", the space temporarily goes down
>> (according to df -h), then it goes back again, even faster than I am
>> freeing it up. Which makes me believe the system catalog is bloated now.
>
> Probably due to all the other operations hitting the database.
>
> Have you tried vacuuming the system catalogs?
>
>>
>> Any advice is appreciated.
>>
>> Thanks a lot!
>>
>
>
> --
> Adrian Klaver
> adrian.klaver@aklaver.com


--
Adrian Klaver
adrian.klaver@aklaver.com