contrib/pg_stat_statements 1202

Here is an update version of contrib/pg_stat_statements.

New modifications from the last version are:
1. New counters in struct Instrumentation.
2. EXPLAIN ANALYZE VERBOSE shows buffer statistics in 'actual' section.
3. Buffer statistics counsters are not reset to zero anymore.

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1. New counters in struct Instrumentation.
[in include/executor/instrument.h, backend/executor/instrument.c]

The following fields are added. They are used by pg_stat_statements
and EXPLAIN ANALYZE VERBOSE. getrusage() is called for each nodes.
Write-counters are not included because I think they are not so useful.

    buffer_gets;    /* # of buffer hits */
    buffer_hits;    /* # of buffer gets */
    buffile_reads;    /* # of buffile reads */
    utime;            /* user time in sec */
    stime;            /* sys time in sec */

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2. EXPLAIN ANALYZE VERBOSE shows buffer statistics in 'actual' section.
[in backend/commands/explain.c]

I borrowed the idea from Vladimir,
"Buffer pool statistics in Explain Analyze".
http://archives.postgresql.org/message-id/1d709ecc0810111624i7419b179v1789b2ca681987c0@mail.gmail.com

Here is an sample output. We'd better to add a linebreak before
the 'actual' section because the line is too wide to display.

=# EXPLAIN ANALYZE VERBOSE SELECT * FROM accounts;
                                                                              QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Seq Scan on accounts  (cost=0.00..2688.29 rows=101829 width=97) (actual time=0.072..119.633 rows=100000 loops=1
gets=1670reads=1638 local_reads=0 CPU=0.06/0.03 sec) 
   Output: aid, bid, abalance, filler
 Total runtime: 209.556 ms
(3 rows)

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3. Buffer statistics counsters are not reset to zero anymore.
[in storage/buffer/bufmgr.c]

ResetBufferUsage() is save the current counters in global variables as
baseline and buffer statistics are measured in difference from them
because the counters are used by struct Instrumentation.

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Comments welcome.

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center