>>>>> "Greg" == Greg Stark <st...@mit.edu> writes:
>> No, because as the pages split, they fill more slowly (because there >> are now more pages). So on average in a large randomly filled index, >> pages spend more time nearer 50% full than 100% full. This is easy >> to demonstrate by creating a table with an indexed float8 column and >> adding batches of random() values to it, checking with pgstatindex >> at intervals - the average leaf density will rarely exceed 70%. >> >> However, worst case conditions can give lower leaf densities; >> obviously the worst case is if the data is loaded in an order and >> quantity that just happens to leave every leaf page recently split. Greg> btree pages don't split 50/50 either. They split biased to assume Greg> the greater side of the split will receive more inserts -- iirc Greg> 70/30. Hmm? The code in _bt_findsplitloc and _bt_checksplitloc doesn't seem to agree with this. (Inserting on the high leaf page is a special case, which is where the fillfactor logic kicks in; that's why sequentially filled indexes are (by default) 90% full rather than 100%. But other pages split into roughly equal halves.) -- Andrew (irc:RhodiumToad) -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
