Improve bad queries (with excessive number of groups) observability #15254
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gortiz
reviewed
Mar 12, 2025
| * But if a single query has 2 different aggregate operators and each one reaches the limit, this will be increased | ||
| * by 2. | ||
| */ | ||
| AGGREGATE_TIMES_NUM_GROUPS_LIMIT_WARNING("times", true), |
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Probably we would also like to have a similar metric but not global
| @@ -123,6 +124,7 @@ protected void processSegments() { | |||
| if (resultsBlock.isNumGroupsLimitReached()) { | |||
| _numGroupsLimitReached = true; | |||
| } | |||
| _numGroups = resultsBlock.getNumGroups(); | |||
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This code can be called more than once. In fact what I think you should be doing is to increase _numGroups by mergedKeys, which is calculated below.
Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #15254 +/- ##
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+ Coverage 61.75% 63.62% +1.87%
- Complexity 207 1459 +1252
============================================
Files 2436 2772 +336
Lines 133233 156301 +23068
Branches 20636 23982 +3346
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+ Hits 82274 99450 +17176
- Misses 44911 49362 +4451
- Partials 6048 7489 +1441
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This PR focuses on improving the observability for queries that may lead to a cluster performance degradation.
In particular, it is focused on group-by queries that lead to an excessive number of groups to be processed.
The following changes are done:
LOGGERstatement that traces all incoming query fromDEBUGtoINFO. Without it, queries are not logged until they are finished which does not help troubleshooting the latest queries against a cluster presenting issues.num.groups.limit.default.warn.factorServer configuration parameter with1.5as default value. When a group by operator detects that more thandefault num.groups.limit * num.groups.limit.default.warn.factorgroups are created, it will emit a warning message such as:Add a
numGroupsattribute to the Broker response, next to the already existingnumGroupsLimitReachedattribute. When the latter istrue, thenumGroupswill match the configured limit. Otherwise, it will show the total number of groups processed by the query. For non-aggregated queries the value will be0.Add a new Server metric named
aggregateTimesNumGroupsLimitWarningwith the number of times the warning message from above has been logged.