Details
-
Bug
-
Status: Closed (View Workflow)
-
Minor
-
Resolution: Fixed
-
10.4.12, 10.5.3
-
None
Description
- Inconsistent and Incorrect rw-lock stats
- There are multiple inconsistency and incorrect way in which rw-lock
stats are calculated.
- shared rw-lock stats:
- "rounds" counter is incremented only once for N rounds done in spin-cycle.
- all rw-lock stats:
- if the spin-cycle is short-circuited then attempts are re-counted.
[if spin-cycle is interrupted, before it completes srv_n_spin_wait_rounds
(default 30) rounds, spin_count (renamed to spin_round_count for better
clarity) is incremented to consider this.
if thread resumes spin-cycle (due to unavailability of the locks)
and is again interrupted or completed spin_count (spin_round_count) is
again incremented with the total count, failing to adjust the previous
attempt increment].
- s/x rw-lock stats:
- spin_loop counter is not incremented at-all instead it is projected
as 0 (in show engine output) and division to calculate spin-round per
spin-loop is adjusted. - as per the original semantics spin_loop counter should be incremented
once per spin_loop execution.
- sx rw-lock stats:
- sx locks increment spin_loop counter but instead of incrementing it once
for spin_loop invocation it does it multiple times based on how many
time spin_loop flow is repeated for same instance post os-wait.
Attachments
Activity
krunalbauskar, thank you! A few notes:
- We try to apply changes to the earliest affected version. I believe that the change should apply to MariaDB 10.2. But your patch is based on 10.5. Can you please rebase it to 10.2?
- Coding style: I prefer to limit the scope of variables. Would ulint j = i; work?
- Can you please open a pull request?
PR submitted: https://github.com/MariaDB/server/pull/1535 (based on 10.2)
Local mtr testing done found to be working (except the known failured re-check it with the http://buildbot.askmonty.org/buildbot/grid?branch=10.2)
Output
-----------
without patch
=============
OS WAIT ARRAY INFO: reservation count 1905259
OS WAIT ARRAY INFO: signal count 424327
RW-shared spins 0, rounds 18226, OS waits 2732
RW-excl spins 0, rounds 11096957, OS waits 178606
RW-sx spins 3204, rounds 83720, OS waits 1918
Spin rounds per wait: 18226.00 RW-shared, 11096957.00 RW-excl, 26.13 RW-sx
with patch
==========
OS WAIT ARRAY INFO: reservation count 1969248
OS WAIT ARRAY INFO: signal count 445870
RW-shared spins 13515, rounds 121096, OS waits 2880
RW-excl spins 1363552, rounds 10484920, OS waits 181852
RW-sx spins 3303, rounds 87907, OS waits 1994
Spin rounds per wait: 8.96 RW-shared, 7.69 RW-excl, 26.61 RW-sx
- Numbers are not directly comparable but just for references
Patch for it could be found here.
https://github.com/mysqlonarm/server/commit/6b21ce184ecc24a03a552eb9b0aad89fc1995be4