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

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