Re: effects of nullifying bytea column on storage

Doesn't vacuum run automatically (or can it be set to run automatically) ?

On Wed, May 11, 2022 at 8:05 PM David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> On Wednesday, May 11, 2022, David Gauthier <dfgpostgres(at)gmail(dot)com> wrote:
>
>> Hi:
>> psql (11.5, server 11.3) on linux
>>
>> I have a table with a bytea column which, of course, contains binary
>> data. After 60 days, I no longer need the binary data but want to retain
>> the rest of the record. Of course it's easy to just update the bytea
>> column to null for the older records. But I can almost imagine this record
>> on disk with a big "hole" in the middle where the bytea data used to be.
>> Is there a PG daemon (the vacuum ?) that will "heal the hole" in time?
>>
>>
> The freshly written record will not have a hole - either by virtue of
> variable width fields taking up basically their actual data space and also
> the fact that null is treated specially in the record format.
>
> For the old row, yes you should read up on the how and why of the vacuum
> command.
>
> David J.
>
>