Neil Conway wrote:
On Thu, 2007-09-20 at 16:08 +0300, Martin Pihlak wrote:
The GUC variable stats_function_level now takes 3 values: on, off and all.


That seems a confusing set of values. Perhaps "off", "pl", and "all"
would be clearer?

Makes sense. It appears that the stats_ prefixed GUC names are deprecated now.
Will rename to "track_functions" and change values to "off", "pl" and
"all". Or should I use "none" instead of "off"?

I'm curious if you've measured the performance overhead of enabling this
functionality.


Just finished a simple benchmark comparing unpatched, "off" and "all":

unpatched usr    sys    total
dummy     21.36  0.68   22.04
rfact     51.52  0.07   51.59
ifact     20.40  0.06   20.45

"off"     usr    sys    total  diff x
dummy     21.59  0.39   21.97  1.00
rfact     52.40  0.06   52.46  1.02
ifact     20.78  0.02   20.8   1.02

"all"     usr    sys    total  diff x
dummy     21.69  35.18  56.87  2.58
rfact     47.83  38.99  86.83  1.68
ifact     20.65  0.36   21.01  1.03

dummy is blank pl/pgsql function (ran 10000000 times). rfact is recursive 
factorial,
ifact is iterative (both ran 1000000 times). Comparing median of 3 runs. The 
usr and
sys values are from log_executor_stats.

It seems that the overhead is unnoticeable if disabled, very visible for 
lightweight
functions and heavy callers. Almost unnoticeable for more compute intensive 
functions.


PS. Would something like this be a canditate for 8.4 inclusion (if polished up)?

It sounds like a useful feature to me.

Good. I'll bring the patch up to date with HEAD.

Regards,
Martin

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