docs/Cluster-VictoriaMetrics.md: clarify the docs about the needed values for -dedup.minScrapeInterval at vmselect during replication when the data is pushed from HA pair

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Aliaksandr Valialkin 2021-07-13 15:29:43 +03:00
parent 2df66dad7b
commit 8d0ec47be9

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@ -364,9 +364,8 @@ so up to 2 `vmstorage` nodes can be lost without data loss. The minimum number o
the remaining 3 `vmstorage` nodes could provide the `-replicationFactor=3` for newly ingested data.
When the replication is enabled, `-replicationFactor=N` and `-dedup.minScrapeInterval=1ms` command-line flag must be passed to `vmselect` nodes.
The `-replicationFactor=N` improves query performance when up to `N-1` vmstorage nodes respond slowly and/or temporarily unavailable. Sometimes `-replicationFactor` at `vmselect` nodes can result in partial responses. See [this issues](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1207) for details.
The `-dedup.minScrapeInterval=1ms` de-duplicates replicated data during queries. It is OK if `-dedup.minScrapeInterval` exceeds 1ms
when [deduplication](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#deduplication) is used additionally to replication.
The `-replicationFactor=N` improves query performance when up to `N-1` vmstorage nodes respond slowly and/or temporarily unavailable, since `vmselect` doesn't wait for responses from up to `N-1` `vmstorage` nodes. Sometimes `-replicationFactor` at `vmselect` nodes can result in partial responses. See [this issues](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1207) for details.
The `-dedup.minScrapeInterval=1ms` de-duplicates replicated data during queries. If duplicate data is pushed to VictoriaMetrics from identically configured [vmagent](https://docs.victoriametrics.com/vmagent.html) instances or Prometheus instances, then the `-dedup.minScrapeInterval` must be set to bigger values according to [deduplication docs](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#deduplication).
Note that [replication doesn't save from disaster](https://medium.com/@valyala/speeding-up-backups-for-big-time-series-databases-533c1a927883),
so it is recommended performing regular backups. See [these docs](#backups) for details.