On 03/29/2011 09:04 AM, Plugge, Joe R. wrote:
Personally, provided you have the room, I would build a new table off to the side and 
then migrate what you need to keep to the new table, when done, and satisfied that you 
have all of the candidate rows, ranem the original to table to "x_tablename" 
and rename the newly created table into place to take over.... if all is good .. simply 
drop the x_tablename table.
This looks attractive but can cause issues if there are views, foreign-keys, etc. that depend on this table.

-----Original Message-----
From: pgsql-admin-ow...@postgresql.org 
[mailto:pgsql-admin-ow...@postgresql.org] On Behalf Of Nic Chidu
Sent: Tuesday, March 29, 2011 10:56 AM
To: pgsql-admin@postgresql.org
Subject: [ADMIN] full vacuum of a very large table

Got a situation where a 130 mil rows (137GB) table needs to be brought down in 
size to  10 mil records (most recent) with the least amount of downtime.

Doing a full vacuum would be faster on:
  - 120 mil rows deleted and 10 mil active (delete most of them then full 
vacuum)
  - 10 mil deleted and 120 mil active. (delete small batches and full vacuum 
after each delete).

Any other suggestions?

The phrase "most recent" leads me to believe this is time-based data. This might be a good time to partition your table to avoid this issue in the future. If you are clever about it (and try it out on a test environment), you might be able to create inherited tables off your main table and then move the "live" data from the parent to the child in unobtrusive sized chunks. When no live data remains in the parent table, truncate the parent table (only).

Moving forward, set up your application/processes to put the data in to the appropriately sized (day?, week?, month? year?) child table. When the time comes, just archive and drop the child.

Cheers,
Steve


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