Page History

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• num-immutable-mem-table
• mem-table-flush-pending
• compaction-pending
• background-errors
• cur-size-active-mem-table
• cur-size-all-mem-tables
• size-all-mem-tables
• num-entries-active-mem-table
• num-entries-imm-mem-tables
• num-deletes-active-mem-table
• num-deletes-imm-mem-tables
• estimate-num-keys
• estimate-table-readers-mem
• num-live-versions
• estimate-live-data-size
• total-sst-files-size
• live-sst-files-size
• estimate-pending-compaction-bytes
• num-running-compactions
• num-running-flushesactual-delayed-write-rate
• estimate-oldest-key-time
• block-cache-capacity
• block-cache-usage
• block-cache-pinned-usage

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• Memtable: Memtables are in-memory write buffers. Each new key-value pair is first written to a memtable and each read looks first into the memtable before it looks on disk. Once a memtable is full it becomes immutable and it is replaced by a new memtable. A background thread flushes a memtable asynchronously to disk. Additionally, memtables can also be flushed manually. RocksDB keeps in memory the currently active memtables, full but not yet flushed memtables, and flushed memtables that are kept around to maintain write history in memory.
• Compaction: From time to time RocksDB needs to clean up the data it stores on disk and bring is LSM tree into a good shape (see https://github.com/facebook/rocksdb/wiki/Compaction). Compactions might block writes and flushes. Additionally, RocksDB offers different compaction algorithms with different properties. Thus, it is a good practise to monitor compactions in RocksDB.
• SST files: SST files are the files in which RocksDB stores the data on disk. SST stands for Sorted Sequence Table.
• Version: A version consists of all the live SST files at one point of time. Once a flush or compaction finishes, a new version is created because the list of live SST files has changed. An old version can be used by on-going read requests or compaction jobs. Old versions will eventually be garbage collected.
• Cache: RocksDB caches data in memory for reads. By default, those caches contain only data blocks, i.e., uncompressed sequences of key-value pairs in sorted order. Therefore this cache is often referred to as block cache. However, users can configure RocksDB to also store index and filter blocks in the cache.

num-immutable-mem-table

Number of immutable memtables that have not yet been flushed. For segmented state stores, the sum of the number of immutable memtables over all segments is reported.

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Total size in bytes of all SST files. For segmented state stores, the sum of the sizes of SST files over all segments is reported.

live-sst-files-size

returns total Total size (in bytes ) of all SST files that belong to the latest LSM tree. sum for For segmented stores

background-errors

returns the accumulated number of background errors. sum for segmented stores

estimate-num-keys

returns estimated number of total keys in the active and unflushed immutable memtables and storage. sum for segmented stores

estimate-table-readers-mem

state stores, the sum of the sizes of SST files over all segments is reported.returns estimated memory used for reading SST tables, excluding memory used in block cache (e.g., filter and index blocks). sum for segmented stores

num-live-versions

returns number Number of live versions. `Version` is an internal data structure. See version_set. h for details. More live versions often mean more SST files are held from being deleted, by iterators or unfinished compactions. sum for For segmented stores

estimate-live-data-size

returns an estimate of the amount of live data in bytes. sum for segmented stores. sum for segmented stores

actual-delayed-write-rate

returns the current actual delayed write rate. 0 means no delay. sum for segmented stores

estimate-oldest-key-time

state stores, the sum of the number of versions over all segments is reported.returns an estimation of oldest key timestamp in the DB. Currently only available for FIFO compaction with compaction_options_fifo.allow_compaction = false. min for segmented stores

block-cache-capacity

returns block Block cache capacity. sum for segmented stores if separate caches are used, otherwise any.

block-cache-usage

returns the memory Memory size for the entries residing in block cache. sum for segmented stores if separate caches are used, otherwise any.

block-cache-pinned-usage

returns the memory Memory size for the entries being pinned. sum for segmented stores if separate caches are used, otherwise any.

estimate-num-keys

Estimated number of total keys in the active and unflushed immutable memtables and storage. For segmented state stores, the sum of the estimated number of keys over all segments is reported.

estimate-table-readers-mem

Estimated memory used for reading SST tables, excluding memory used in block cache (e.g., filter and index blocks). sum for segmented stores

estimate-oldest-key-time

Estimated oldest key timestamp in the RocksDB instance. This metric is currently only available for FIFO compaction with compaction_options_fifo.allow_compaction = false. For segmented state stores, the minimum of the estimated oldest key timestamp over all segments is reported.

background-errors

Accumulated number of background errors. For segmented state stores, the sum of the number of background errors over all segments is reported.

memtables-size

Memory usage of all mem-tables. Mem-tables are in-memory write buffers. Each new key-value pair is first written to a mem-table and each read looks first into the mem-table before it looks on disk. Once a mem-table is full it becomes immutable and it is replaced by a new mem-table. A background thread flushes a mem-table asynchronously to disk. Additionally, mem-tables can also be flushed manually. RocksDB keeps in memory the currently active mem-tables, full but not yet flushed mem-tables, and flushed mem-tables that are kept around to maintain write history in memory.

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