On 10/12/13 17:18, Claudio Freire wrote:
On Tue, Dec 10, 2013 at 12:13 AM, Mark Kirkwood
Just one more...
The Intel 520 with ext4:
Without patch: ANALYZE pgbench_accounts 5s
With patch: ANALYZE pgbench_accounts 1s
And double checking -
With patch, but effective_io_concurrency = 1: ANALYZE pgbench_accounts 5s
These results look more like Heikki's. Which suggests more benefit on SSD
than spinning disks. Some more data points (apart from mine) would be good
to see tho.
Assuming ANALYZE is sampling less than 5% of the table, I'd say
fadvising will always be a win.
I'd also suggest higher e_i_c for rotating media. Rotating media has
longer latencias, and e_i_c has to be computed in terms of latency,
rather than "spindles" when doing prefetch.
For backward index scans, I found the optimum number for a single
spindle to be about 20.
Yeah - was just fooling about with this on the velociraptor, looks like
somewhere in the 20's works well.
eff_io_concurrency | analyze time (s)
8 | 43
16 | 40
24 | 36
32 | 35
64 | 35
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