Re: Recommendation to run vacuum FULL in parallel

On 4/3/19 3:45 PM, Perumal Raj wrote:

Hi Stephen 

Thanks for the response ,

Version : 9.2 

We never ran VACUUM FULL in the past, All we are doing just manual vacuum ( Weekly ) .

Based on the Observation ( test run ) , we were able to reclaim 150 GB out of 500 GB .

We are heading to a planned down time soon , So thinking  to run FULL during that time .

Reason behind to run FULL : 1. Reclaim unused space which postgres never using it.

Did you purge a lot of records?

                                                2. Considering  FULL may increase the performance.

Maybe. But choose your tables wisely.

                                                3. Daily backup size and time  will be reduced after reclaiming 150GB.

How are you currently performing backups?  (The size won't change if you're using pg_dump, and it won't change much if you're using pgbackrest with the compression option -- thought it will probably run faster.)

Bottom line:

1. choose your tables wisely.
2. make sure you have enough disk space.
3. Either autovacuum more aggressively or explicitly vacuum certain tables from a cron job.

Thanks,

Raj

On Wed, Apr 3, 2019 at 1:16 PM Stephen Eilert <contact@stepheneilert.com> wrote:

> Ideally VACUUM FULL should not require a giant lock on the table.

It is a massively expensive operation, regardless. Not sure if it is something you want to run in production outside a maintenance window.

I would argue that frequent vacuum full is an antipattern. This will become a matter of superstition in your company.

If db size growth is a problem, make autovacuum more agressive. Or run your manual vacuum job (not full) more often than a week. Daily, if you have to. This will not reclaim disk space as reported by the OS, but it should make the space available for new row versions, so db should mostly stop growing from the OS point of view(mostly, because you may be adding new data, right?). If it is still a problem, then there may be something else going on.

Which PG version is that?

— Stephen

On Apr 3, 2019, 10:02 AM -0700, Perumal Raj <perucinci@gmail.com>, wrote:

Hi All

Thanks for all your valuable  inputs,

Here is some more data,

Though we have 150 GB free space spread across 500 Tables , Every alternative day DB is growing with 1 GB rate.

Also,We have manual vacuum job scheduled to run weekly basis, So seems to be space is not reusing all the time ?

So conclude the requirement here , The only way to parallelism is multiple script. And no need to do REINDEX exclusively.

Question : Do we need to consider  Table dependencies while preparing script in order to avoid table locks during vacuum full ?

At present Maintenance work memory set to 20 GB.

Question : Do we need to tweak any other parameters ?

Note: 

We are planning this activity with Application Downtime only.

Let me know if i missed anything.

Regards,

Raj

 

On Wed, Apr 3, 2019 at 8:42 AM rihad <rihad@mail.ru> wrote:

> And future updates can reuse it, too (an update is very similar to an
> insert+delete).


Hm, then it's strange our DB takes 6 times as much space compared to
freshly restored one (only public schema is considered).

> Not if autovacuum has a chance to run between updates.

Ours is run regularly, although we had to tweak it down not to interfere
with normal database activity, so it takes several hours each run on the
table. We did that by setting autovacuum_vacuum_scale_factor = 0.05 from
default 0.2.