Re: Idea for getting rid of VACUUM FREEZE on cold pages

On 26/05/10 21:35, Josh Berkus wrote:
> On 5/25/10 10:04 PM, Heikki Linnakangas wrote:
>> On 25/05/10 23:56, Josh Berkus wrote:
>>> Do we get a bit in the visibility map for a page which has aborted
>>> transaction rows on it?
>>
>> If there's a tuple with an aborted xmin on a page, the bit in the
>> visibility map is not set. A tuple with aborted xmax doesn't matter.
>
> Then it seems like pages in the visibility map, at least, would not need
> to be vacuumed or frozen.  Do pages persist in the visibility map
> indefinitely?

In theory, until any tuple on the page is inserted/updated/deleted 
again. However, we've been operating on the assumption that it's always 
safe to clear any bit in the visibility map, without affecting 
correctness. I would not like to give up that assumption, it makes life 
easier.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com