On 8/8/07, Gregory Stark <stark@enterprisedb.com> wrote:
It seems that previously percentage of tuples made sense because dead tuples
took about the same amount of space as new tuples that need that space. But
line pointers take much less space than the new tuples so the number of dead
line pointers we need before we can recover a useful amount of space depends
on the ratio of line pointer size to tuple size.
Perhaps we should be gathering "bytes of dead tuples" in pg_stat not just
n_dead_tuples.
This is a good idea. Alternatively, we can guess percentage of dead space
using the average tuple size, number of dead tuples and number of reltuples.
Another thing to worry about is index bloats. Even though a redirect-dead
line pointer takes only 4 bytes in the heap, the associated dead space
in the index is as large as any other index tuple and the index
might be in a need for vacuum.
Thanks,
Pavan
--
Pavan Deolasee
EnterpriseDB
http://www.enterprisedb.com