On 22.07.2011 12:38, Alexander Korotkov wrote:
Patch with my try to detect ordered datasets is attached. The implemented idea is desribed below. Index tuples are divided by chunks of 128. On each chunk we measure how much leaf pages where index tuples was inserted don't match those of previous chunk. Based on statistics of several chunks we estimate distribution of accesses between lead pages (exponential distribution law is accumed and it's seems to be an error). After that we can estimate portion of index tuples which can be processed without actual IO. If this estimate exceeds threshold then we should switch to buffering build. Now my implementation successfully detects randomly mixed datasets and well ordered datasets, but it's seems to be too optimistic about intermediate cases. I believe it's due to wrong assumption about distribution law. Do you think this approach is acceptable? Probably there are some researches about distribution law for such cases (while I didn't find anything relevant in google scholar)?
Great! It would be nice to find a more scientific approach to this, but that's probably fine for now. It's time to start cleaning up the patch for eventual commit.
You got rid of the extra page pins, which is good, but I wonder why you still pre-create all the GISTLoadedPartItem structs for the whole subtree in loadTreePart() ? Can't you create those structs on-the-fly, when you descend the tree? I understand that it's difficult to update all the parent-pointers as trees are split, but it feels like there's way too much bookkeeping going on. Surely it's possible to simplify it somehow..
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
