Previously entries which were accessed only 1 time weren't cached.
It has been appeared that some rarely executed heavy queries may read indexdb block twice
in a row instead of once. There is no need in caching such a block then.
This change should eliminate cache size spikes for indexdb/dataBlocks when such heavy queries are executed.
Expose -blockcache.missesBeforeCaching command-line flag, which can be used for fine-tuning
the number of cache misses needed before storing the block in the caching.
This should improve data ingestion speed if time series samples are ingested with interval bigger than 2 minutes.
The actual interval could exceed 2 minutes if the original interval between samples doesn't exceed 2 minutes
in the case of slow inserts. Slow inserts may appear in the following cases:
* Big number of new time series are pushed to VictoriaMetrics, so they couldn't be registered in 2 minutes.
* MetricName->tsid cache reset on indexdb rotation or due to unclean shutdown.
In this case VictoriaMetrics needs to load MetricName->tsid entries for all the incoming series from IndexDB.
IndexDB uses the block cache for increasing lookup performance. If the cache has no the needed block,
then IndexDB reads and unpacks the block from disk. This requires an extra disk read IO and CPU.
See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1401
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2007
This also should increase performance for periodically executed queries with intervals from 2 minutes to 5 minutes.
See the previous similar commit - 43103be011
It is possible that the timeout can be increased further. Let's collect production numbers for this change
so the timeout could be adjusted further.
- Optimize Cache.RemoveBlocksFromPart(), so it doesn't need to iterate over all the cached blocks.
- Cache blocks if there were no cache misses during the last 2 minutes.
This may be the case when new blocks are added simultaneously to the storage and to the cache.
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2007
