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doc: Improve descriptions of tup_returned and tup_fetched in pg_stat_database 

Previously the descriptions of tup_returned and tup_fetched columns
in pg_stat_database view were confusing. This commit improves them
so that they represent the following formulas of those columns
more accurately.

* pg_stat_database.tup_returned
    = sum(pg_stat_all_tables.seq_tup_read)
    + sum(pg_stat_all_indexes.idx_tup_read)

* pg_stat_database.tup_fetched
    = sum(pg_stat_all_tables.idx_tup_fetch)

In these formulas, note that the counters for some system catalogs
like pg_database shared across all databases of a cluster are excluded
from the calculations of sum.

Author: Masahiro Ikeda
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/9eeeccdb-5dd7-90f9-2807-a4b5d2b76ca3@oss.nttdata.com
This commit is contained in:
Fujii Masao 2021-06-30 20:57:07 +09:00
parent 61d599ede7
commit 3465c8a869
1 changed files with 2 additions and 2 deletions
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doc/src/sgml/monitoring.sgml
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@ -3712,7 +3712,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>tup_returned</structfield> <type>bigint</type>
</para>
<para>
Number of rows returned by queries in this database
Number of live rows fetched by sequential scans and index entries returned by index scans in this database
</para></entry>
</row>
@ -3721,7 +3721,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>tup_fetched</structfield> <type>bigint</type>
</para>
<para>
Number of rows fetched by queries in this database
Number of live rows fetched by index scans in this database
</para></entry>
</row>