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• write-waiting-time-(avg|total) [ms]
• bytes-written-rate [bytes/s]
• bytes-written-total [bytes]
• bytes-read-rate [bytes/s]
• bytes-read-total [bytes]
• memtable-hit-rate
• block-cache-bytes-read-rate [bytes/s]
• block-cache-bytes-written-rate [bytes/s]
• block-cache-hit-rate
• bytes-flushed-rate [bytes/s]
• bytes-flushed-total [bytes]
• flush-time-(avg|min|max) [ms]
• bytes-read-compaction-rate [bytes/s]
• bytes-written-compaction-rate [bytes/s]
• compaction-time-(avg|min|max) [ms]
• num-open-files
• num-file-errors-total

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When data is put into RocksDB, the data is written into a in-memory tree data structure called memtable. When the memtable is almost full, data in the memtable is flushed to disk by a background process. The data on disk needs to be reorganised from time to time. This reorganisatoin reorganisation is called compaction and is also performed by a background process. During flush and compaction a write to the database might need to wait until these processes finish. These metrics measure the average and total waiting time of a write process until flush and compaction finish.

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If memtable-hit-rate is to high with respect to for the given workload, the memtable may be too small.

block-cache-hit-rate

If data is not found in the memtable, the block cache is consulted. This metric measures the number of hits with respect to the number of all lookups into the block cache. The formula for this metric is the same as for memtable-hit-rate.

If block-cache-hit-rate is to high for the given workload, the block-cache-hit-rate needs maybe some tuning.

bytes-flushed-(rate|total)

As explained for write-waiting-time-(avg|total), when the memtable is almost full, the memtable is emptied and flushed to disk. These metrics measure the number of bytes flushed to disk.

The metrics show IO load produced by the RocksDB instance.   

Compatibility, Deprecation, and Migration Plan

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