>>>>> "Jeff" == Jeff Janes <jeff.ja...@gmail.com> writes:
Jeff> But shouldn't that still leave us with a 75% full index, rather Jeff> than slightly over 50% full? Average is usually about 67%-70%. (For capacity estimation I always assume 66% for a non-sequentially-filled btree.) Jeff> The leaf pages start at 50%, grow to 100%, then split back to Jeff> 50%, then grow back to 100%. So the average should be about 75%. 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. -- 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
