From 5d27642106a67fad669f72f48158905d1c8c564f Mon Sep 17 00:00:00 2001 From: Aliaksandr Valialkin Date: Fri, 13 Nov 2020 18:33:53 +0200 Subject: [PATCH] docs/Single-server-VictoriaMetrics.md: explain why recently inserted data may be unavailable for querying for a few seconds --- README.md | 6 ++++++ docs/Single-server-VictoriaMetrics.md | 6 ++++++ 2 files changed, 12 insertions(+) diff --git a/README.md b/README.md index 4f9c9426c..e96ebea1d 100644 --- a/README.md +++ b/README.md @@ -1209,6 +1209,12 @@ VictoriaMetrics also exposes currently running queries with their execution time * It is recommended inspecting logs during troubleshooting, since they may contain useful information. +* VictoriaMetrics buffers incoming data in memory for up to a few seconds before flushing it to persistent storage. + This may lead to the following "issues": + * Data becomes available for querying in a few seconds after inserting. + * The last few seconds of inserted data may be lost on unclean shutdown (i.e. OOM, `kill -9` or hardware reset). + See [this article for technical details](https://valyala.medium.com/wal-usage-looks-broken-in-modern-time-series-databases-b62a627ab704). + * If VictoriaMetrics works slowly and eats more than a CPU core per 100K ingested data points per second, then it is likely you have too many active time series for the current amount of RAM. VictoriaMetrics [exposes](#monitoring) `vm_slow_*` metrics, which could be used as an indicator of low amounts of RAM. diff --git a/docs/Single-server-VictoriaMetrics.md b/docs/Single-server-VictoriaMetrics.md index 4f9c9426c..e96ebea1d 100644 --- a/docs/Single-server-VictoriaMetrics.md +++ b/docs/Single-server-VictoriaMetrics.md @@ -1209,6 +1209,12 @@ VictoriaMetrics also exposes currently running queries with their execution time * It is recommended inspecting logs during troubleshooting, since they may contain useful information. +* VictoriaMetrics buffers incoming data in memory for up to a few seconds before flushing it to persistent storage. + This may lead to the following "issues": + * Data becomes available for querying in a few seconds after inserting. + * The last few seconds of inserted data may be lost on unclean shutdown (i.e. OOM, `kill -9` or hardware reset). + See [this article for technical details](https://valyala.medium.com/wal-usage-looks-broken-in-modern-time-series-databases-b62a627ab704). + * If VictoriaMetrics works slowly and eats more than a CPU core per 100K ingested data points per second, then it is likely you have too many active time series for the current amount of RAM. VictoriaMetrics [exposes](#monitoring) `vm_slow_*` metrics, which could be used as an indicator of low amounts of RAM.