Re: [GENERAL] Question about TOAST table - PostgreSQL 9.2

Patrick B wrote:
> I have a database which is 4TB big. We currently store binary data in a bytea data type column
> (seg_data BYTEA). The column is behind binary_schema and the files types stored are: pdf, jpg, png.

> Questions:
> 
> 1 - If I take out 500GB of bytea data ( by updating the column seg_data and setting it to null ), will
> I get those 500GB of free disk space? or do I need to run vacuum full or either pg_dump?

You'll need VACUUM (FULL) or dump/restore.

> 2 - If I choose going ahead with VACUUM FULL, I have 3 streaming replication slaves, Will I need to
> run the vacuum full on them too?

No, and indeed you cannot.
The changes made by VACUUM on the primary will be replicated.

> 3 - [2] vacuum full needs some free disk space as same size as the target table. It locks the table
> (cannot be used while running vacuum full) and a REINDEX might be needed after. AM I right?

It locks the table for all concurrent access, but a REINDEX is not necessary, as the
indexes are rewritten as well.

Yours,
Laurenz Albe