Re: GiST insert algorithm rewrite

On 13.12.2010 19:48, Tom Lane wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>> On 13.12.2010 19:19, Greg Stark wrote:
>>> If it's only the backup blocks that matter couldn't you generate noop
>>> WAL records with just the full page image in them. Once all those are
>>> generated then generate the actual split operation and since all the
>>> pages have been written to wal since the last checkpoint they won't
>>> need any backup block slots.
>>>
>>> This would require surpressing any checkpoints between writing the
>>> first backup block and the final operation record. That might be
>>> pretty hard to do cleanly.
>
>> That would work, but it brings us back to square one
>
> Yeah. Wouldn't the original page-split record have been carrying full
> page images already?

Yes.

BTW, the original split record doesn't run into the limit because it
doesn't use the backup-block mechanism, it contains all the tuples for
all the pages in the main payload.

> (And if so, why didn't we have this problem in the
> previous implementation?)

In the previous implementation, the NSN was updated immediately in the
page split record, and there was no follow-right flag to clear. So the
child pages didn't need to be updated when the downlinks are inserted.

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