How do we handle this situation? We go to insert a record in the heap, find no free space, so we extend the table and insert it into a new page. Then we insert an index entry pointing to the new tuple. Then some other backend (or bgwriter) comes along and decides the index page is a good candidate for eviction and forces an xlog buffer flush for that buffer. Then the system crashes.
Now when the system comes back up the index will have a pointer to a page beyond the end of the heap. Even if we have a WAL log entry for the extension the index pointer would be pointing to a zeroed block so vacuum would never get the chance to note the tuple is dead and remove the index pointer. I know there's some special code in lazyvacuum to handle zeroed pages but I don't think it does anything special to note those zeroed pages and check index entries against them, does it? -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
