RE: pg_wal fills up on big update query

Hi Rob,

Thanks, I will try.

It’s a bit of a bummer though, because I just started to use flywaydb to
manage migrations, and it wraps all migrations into a single transaction.

So I have to do this outside of the tool.

Best Regards,

Daniel

*From:* Rob Sargent [mailto:robjsargent(at)gmail(dot)com]
*Sent:* Wednesday, August 7, 2019 4:22 PM
*To:* Daniel Fink (PDF) <daniel(dot)fink(at)pdf(dot)com>
*Cc:* pgsql-general(at)lists(dot)postgresql(dot)org
*Subject:* Re: pg_wal fills up on big update query

On Aug 7, 2019, at 7:34 AM, Daniel Fink (PDF) <daniel(dot)fink(at)pdf(dot)com> wrote:

Hi all,

I have a migration where I

· Add a new nullable column to a table

· update almost every row in this big table (8 million rows) from
another table where I set this new column

I have also a replication setup running.

The database has a size of around 20GB.

While the migration is running, it more than doubles is size and fills up
all space.

Then the migration fails and is rolled back.

What is the best way of keeping this from happening?

My current idea is to lock both tables completely from access (the queried
and the updated one) so that postgresql does not have to ensure isolation
for concurrent queries by keeping a copy of each row.

Is my thinking here correct?

Thanks in advance and Best Regards,

Do the update in small chunks

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