On T, 2005-09-27 at 17:57 -0500, Jim C. Nasby wrote: > On Tue, Sep 27, 2005 at 02:47:46PM -0400, Jan Wieck wrote: > > On 9/24/2005 8:17 PM, Jim C. Nasby wrote: > > > > >Would it be difficult to vacuum as part of a dump? The reasoning behind > > >this is that you have to read the table to do the dump anyway, > > > > I think aside from what's been said so far, it would be rather difficult > > anyway. pg_dump relies on MVCC and requires to run in one transaction to > > see a consistent snapshot while vacuum jiggles around with transactions > > in some rather non-standard way. > > Is this true even if they were in different connections? > > My (vague) understanding of the vacuum process is that it first vacuums > indexes, and then vacuums the heap.
actually (lazy) vacuum does this 1) scan heap, collect ctids of rows to remove 2) clean indexes 3) clean heap > Since we don't dump indexes, there's > nothing for backup to do while those are vacuumed, so my idea is: > > pg_dump: > foreach (table) > spawn vacuum > wait for vacuum to hit heap > start copy > wait for analyze to finish > next; probably the first heap scan of vacuum would go faster than dump as it does not have to write out anything, and the second scan ( nr 3 in above list ) would be either faster or slower, as it has to lock each page and rearrange tuples there. so it would be very hard to synchronize vacuum with either of them. -- Hannu Krosing <[EMAIL PROTECTED]> ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
