Hi,
I found that pgBufferUsage.blk_{read|write}_time are zero although there are pgBufferUsage.local_blks_{read|written}. For example, when you run (track_io_timing should be on):
CREATE EXTENSION pg_stat_statements;
CREATE TEMP TABLE example_table (id serial PRIMARY KEY, data text);
INSERT INTO example_table (data) SELECT 'Some data'
FROM generate_series(1, 100000);
UPDATE example_table SET data = 'Updated data';
SELECT query, local_blks_read, local_blks_written,
blk_read_time, blk_write_time FROM pg_stat_statements
WHERE query like '%UPDATE%';on master:
query | UPDATE example_table SET data = $1
local_blks_read | 467
local_blks_written | 2087
blk_read_time | 0
blk_write_time | 0
There are two reasons of that:
1- When local_blks_{read|written} are incremented, pgstat_count_io_op_time() is called with IOOBJECT_TEMP_RELATION. But in pgstat_count_io_op_time(), pgBufferUsage.blk_{read|write}_time increments are called only when io_object is IOOBJECT_RELATION. The first patch attached fixes that.
2- in ExtendBufferedRelLocal() and in ExtendBufferedRelShared(), extend calls increment local_blks_written and shared_blks_written respectively. But these extends are not counted while calculating the blk_write_time. If there is no specific reason to not do that, I think these extends needs to be counted in blk_write_time. The second patch attached does that.
Results after applying first patch:
query | UPDATE example_table SET data = $1
local_blks_read | 467
local_blks_written | 2087
blk_read_time | 0.30085
blk_write_time | 1.475123
Results after applying both patches:
query | UPDATE example_table SET data = $1
local_blks_read | 467
local_blks_written | 2087
blk_read_time | 0.329597
blk_write_time | 4.050305
Any kind of feedback would be appreciated.
Regards,
Nazir Bilal Yavuz
Microsoft
