Re: [HACKERS] NDirectFileRead and Write

Here is a patch to user NDirectFileRead/Write counters to get I/O counts
in BufFile module. We can see the counters when log_statement_stats is on.

The information is different from trace_sort; trace_sort shows used blocks
in external sort, and log_statement_stats shows how many I/Os are submitted
during sorts.

I wrote:
> I'd like to use NDirectFileRead and NDirectFileWrite statistics counters
> for counting reads and writes in BufFile. They are defined, but not used
> now. BufFile is used for tuple sorting or materializing, so we could use
> NDirectFileRead/Write to retrieve how many I/Os are done in temp tablespace.

=# SET client_min_messages = log;
=# SET trace_sort = on;
=# SET log_statement_stats = on;
=# EXPLAIN ANALYZE SELECT * FROM generate_series(1, 1000000) AS i ORDER BY i;
LOG: begin tuple sort: nkeys = 1, workMem = 1024, randomAccess = f
LOG: switching to external sort with 7 tapes: CPU 0.09s/0.26u sec elapsed 0.35 sec
LOG: performsort starting: CPU 0.48s/1.68u sec elapsed 2.20 sec
LOG: finished writing final run 1 to tape 0: CPU 0.48s/1.70u sec elapsed 2.21 sec
LOG: performsort done: CPU 0.48s/1.70u sec elapsed 2.21 sec
LOG: external sort ended, 2444 disk blocks used: CPU 0.79s/2.23u sec elapsed 3.06 sec
LOG: QUERY STATISTICS
DETAIL: ! system usage stats:
! 3.078000 elapsed 2.234375 user 0.812500 system sec
! [3.328125 user 1.281250 sys total]
! buffer usage stats:
! Shared blocks: 0 read, 0 written, buffer hit rate = 0.00%
! Local blocks: 0 read, 0 written, buffer hit rate = 0.00%
! Direct blocks: 5375 read, 5374 written
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
Sort (cost=62.33..64.83 rows=1000 width=4) (actual time=2221.485..2743.831 rows=1000000 loops=1)
Sort Key: i
Sort Method: external sort Disk: 19552kB
-> Function Scan on generate_series i (cost=0.00..12.50 rows=1000 width=4) (actual time=349.065..892.907 rows=1000000 loops=1)
Total runtime: 3087.305 ms
(5 rows)

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