On 7/22/15 6:58 AM, Amit Langote wrote:
On Wed, Jul 22, 2015 at 8:19 PM, Alvaro Herrera
<alvhe...@2ndquadrant.com> wrote:
Not sure what Jim meant. Maybe he meant to be aware of when spilling to
disk happens? Obviously, things become slower, so maybe you need to
consider it for progress reporting purposes.
Perhaps the m_w_m determines how many dead tuples lazy_scan_heap() can
keep track of before doing a lazy_vacuum_indexes() +
lazy_vacuum_heap() round. Smaller the m_w_m, more the number of index
scans, slower the progress?
Yes. Any percent completion calculation will have to account for the
case of needing multiple passes through all the indexes.
Each dead tuple requires 6 bytes (IIRC) of maintenance work mem. So if
you're deleting 5M rows with m_w_m=1MB you should be getting many passes
through the indexes. Studying the output of VACUUM VERBOSE will confirm
that (or just throw a temporary WARNING in the path where we start the
scan).
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Data in Trouble? Get it in Treble! http://BlueTreble.com
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