RE: UPDATE on 20 Million Records Transaction or not?

Hello List,
PostgreSQL 11.8 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (R
ed Hat 4.4.7-23), 64-bit

I am planning an update on a table with 20Million records, I have been researching the best practices. I will remove all indexes and foreign keys prior to the update, however I am not sure if I should use a transaction or not.
My thought process is that a transaction would be easier to recover if something fails, however it would take more time to write to the WAL log in a transaction.

>Are you updating every row in the table?
No I am using an update like so: UPDATE members SET regdate='2038-01-18' WHERE regdate='2020-07-07'
DB=# select count(*) from members where regdate = '2020-07-07';
count
----------
17333090
(1 row)

>Are you updating indexed fields? (If not, then leave the indexes and FKs, since they won't be touched.)
Just checked regdate is not indexed so I will leave them in place.

Would it make sense to make a back up of the table then execute update without a transaction?

>Always make a backup.
Agreed

How would you guys do it?

>It depends on what percentage of the rows are being updated, which columns are being updated and how big the records are.
Please see above, thanks

Jason Ralph

From: Ron <ronljohnsonjr(at)gmail(dot)com>
Sent: Tuesday, June 23, 2020 10:57 AM
To: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Re: UPDATE on 20 Million Records Transaction or not?

On 6/23/20 8:32 AM, Jason Ralph wrote:

Hello List,
PostgreSQL 11.8 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (R
ed Hat 4.4.7-23), 64-bit

I am planning an update on a table with 20Million records, I have been researching the best practices. I will remove all indexes and foreign keys prior to the update, however I am not sure if I should use a transaction or not.
My thought process is that a transaction would be easier to recover if something fails, however it would take more time to write to the WAL log in a transaction.

Are you updating every row in the table?

Are you updating indexed fields? (If not, then leave the indexes and FKs, since they won't be touched.)

Would it make sense to make a back up of the table then execute update without a transaction?

Always make a backup.

How would you guys do it?

It depends on what percentage of the rows are being updated, which columns are being updated and how big the records are.

--
Angular momentum makes the world go 'round.
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