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docs/Troubleshooting.md: refer to subqueries doc, since this is the most frequent source of improperly consutructed queries

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Aliaksandr Valialkin 2022-06-30 15:09:35 +03:00
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@ -29,6 +29,11 @@ If you see unexpected or unreliable query results from VictoriaMetrics, then try
- Remove the outer `rate`: `http_requests_total`. Additional label filters may be added here in order - Remove the outer `rate`: `http_requests_total`. Additional label filters may be added here in order
to reduce the number of returned series. to reduce the number of returned series.
Sometimes the query may be improperly constructed, so it returns unexpected results.
It is recommended reading and understanding [MetricsQL docs](https://docs.victoriametrics.com/MetricsQL.html),
especially [subqueries](https://docs.victoriametrics.com/MetricsQL.html#subqueries)
and [rollup functions](https://docs.victoriametrics.com/MetricsQL.html#rollup-functions) sections.
2. If the simplest query continues returning unexpected / unreliable results, then export raw samples 2. If the simplest query continues returning unexpected / unreliable results, then export raw samples
for this query via [/api/v1/export](https://docs.victoriametrics.com/#how-to-export-data-in-json-line-format) for this query via [/api/v1/export](https://docs.victoriametrics.com/#how-to-export-data-in-json-line-format)
on the given `[start..end]` time range and check whether they are expected: on the given `[start..end]` time range and check whether they are expected:
@ -179,7 +184,7 @@ Some queries may take more time and resources (CPU, RAM, network bandwidth) than
VictoriaMetrics logs slow queries if their execution time exceeds the duration passed VictoriaMetrics logs slow queries if their execution time exceeds the duration passed
to `-search.logSlowQueryDuration` command-line flag. to `-search.logSlowQueryDuration` command-line flag.
VictoriaMetrics also provides `/api/v1/status/top_queries` endpoint, which returns VictoriaMetrics also provides `/api/v1/status/top_queries` endpoint, which returns
queries took the most time to execute. queries that took the most time to execute.
See [these docs](https://docs.victoriametrics.com/#prometheus-querying-api-enhancements) for details. See [these docs](https://docs.victoriametrics.com/#prometheus-querying-api-enhancements) for details.
There are the following solutions exist for slow queries: There are the following solutions exist for slow queries:
@ -196,6 +201,8 @@ There are the following solutions exist for slow queries:
See also [this article](https://valyala.medium.com/how-to-optimize-promql-and-metricsql-queries-85a1b75bf986), See also [this article](https://valyala.medium.com/how-to-optimize-promql-and-metricsql-queries-85a1b75bf986),
which explains how to determine and optimize slow queries. which explains how to determine and optimize slow queries.
In practice many slow queries are generated because of improper use of [subqueries](https://docs.victoriametrics.com/MetricsQL.html#subqueries).
## Out of memory errors ## Out of memory errors