Re: UPDATE on 20 Million Records Transaction or not?

[Ron <ronljohnsonjr@xxxxxxxxx>]

    I'd make a copy of the table, and test how long the various methods
    take.

On 6/23/20 10:17 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?

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@xxxxxxxxx>
Sent: Tuesday, June 23, 2020 10:57 AM
To: pgsql-general@xxxxxxxxxxxxxxxxxxxx
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.

This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission. If verification is required please request a hard-copy version.

--
Angular momentum makes the world go 'round.