On 4/22/2005 3:53 PM, Tom Lane wrote:
Jan Wieck <[EMAIL PROTECTED]> writes:tuples fetched is the number of raw, possibly dead tuples fetched from the heap. Tuples returned is the number of alive tuples ... IIRC.
No, count_heap_fetch only counts tuples that have already passed the snapshot test. It could be that the places where the counts are actually bumped don't line up with your original vision for the stats design.
For a regular index scan, it seems to make sense to count (a) number of TIDs returned by the index AM, and (b) number of tuples returned by the IndexScan node. There are several intermediate steps * does the tuple pass the snapshot test * does the tuple pass any indexqual rechecks (for lossy indexes) * does the tuple pass any additional non-index restriction conditions that are being enforced at the scan level
Now that you say it ... yes. The whole stats stuff was intended originally to find "DB tuning hints". A large number of tuples returned by index scan and filtered out by additional non-index restrictions indicate that there might be another multicolumn index missing.
Jan
-- #======================================================================# # It's easier to get forgiveness for being wrong than for being right. # # Let's break this rule - forgive me. # #================================================== [EMAIL PROTECTED] #
---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
