Erik Jones wrote: > Decibel! wrote: >> I should mention that if you can handle splitting the >> update into multiple transactions, that will help a >> lot since it means you won't be doubling the size of >> the table. > > As I mentioned above, when you do an update you're actually inserting a > new row and deleting the old one. That deleted row is still considered > part of the table (for reasons of concurrency, read up on the > concurrency chapter in the manual for the details) and once it is no > longer visible by any live transactions can be re-used by future > inserts. So, if you update one column on every row of a one million row > table all at once, you have to allocate and write out one million new > rows. But, if you do the update a quarter million at a time, the last > three updates would be able to re-use many of the rows deleted in > earlier updates. Only if you vacuum between the updates. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
