Autovacuum log messges re: index scans

[Wells Oliver <wells.oliver@xxxxxxxxx>]

Can someone point me to more detail about this sort of message which comes from the automatic vacuum log messages?

	index scan needed: 309538 pages from table (17.70% of total) had 27187607 dead item identifiers removed

I am trying to figure out what the "dead item identifiers" means exactly and what's happening here in this step. Does it indicate an index was somehow optimized?

I do see lines following this that pertain to individual indexes, what can I glean exactly from these? e.g.

	index "myidx": pages: 169980 in total, 9410 newly deleted, 9681 currently deleted, 271 reusable

Thank you.

--

Wells Oliver
wells.oliver@xxxxxxxxx