On 2021/05/17 18:58, Masahiro Ikeda wrote:
On 2021/05/17 15:32, Fujii Masao wrote:
On 2021/05/14 17:00, Masahiro Ikeda wrote:
Hi,
I worried the difference between "tup_returned" and "tup_fetched" in
pg_stat_database. I assumed that "tup_returned" means the number of tuples
that returned to clients. Of course, this is wrong.
- Number of rows returned by queries in this database
+ Number of live rows returned by sequential scans of queries in this
database
- Number of rows fetched by queries in this database
+ Number of live rows fetched by index scan of queries in this database
I found the following comments in pgstat.h. So maybe even these
new descriptions are incorrect?
* Note: for a table, tuples_returned is the number of tuples successfully
* fetched by heap_getnext, while tuples_fetched is the number of tuples
* successfully fetched by heap_fetch under the control of bitmap indexscans.
* For an index, tuples_returned is the number of index entries returned by
* the index AM, while tuples_fetched is the number of tuples successfully
* fetched by heap_fetch under the control of simple indexscans for this index.
Oh, Thanks!
I updated the sentences using the descriptions of
"pg_stat_all_tables.seq_tup_read", "pg_stat_all_tables.idx_tup_fetch", and
"pg_stat_all_index.idx_tup_read".
- Number of rows returned by queries in this database
+ Number of rows returned by queries in this database. The rows
correspond to the live rows fetched by sequential scans and index entries
returned by scans on indexes
This is still not correct because this counter is incremented even when
other scan like TidScan happens?
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
