Configure RocksDB state store on Azure Databricks

  • Article

You can enable RocksDB-based state management by setting the following configuration in the SparkSession before starting the streaming query.

spark.conf.set(
  "spark.sql.streaming.stateStore.providerClass",
  "com.databricks.sql.streaming.state.RocksDBStateStoreProvider")

You can enable RocksDB on Delta Live Tables pipelines. See Optimize pipeline configuration for stateful processing.

Enable changelog checkpointing

In Databricks Runtime 13.3 LTS and above, you can enable changelog checkpointing to lower checkpoint duration and end-to-end latency for Structured Streaming workloads. Databricks recommends enabling changelog checkpointing for all Structured Streaming stateful queries.

Traditionally RocksDB State Store snapshots and uploads data files during checkpointing. To avoid this cost, changelog checkpointing only writes records that have changed since the last checkpoint to durable storage."

Changelog checkpointing is disabled by default. You can enable changelog checkpointing in the SparkSession level using the following syntax:

spark.conf.set(
  "spark.sql.streaming.stateStore.rocksdb.changelogCheckpointing.enabled", "true")

You can enable changelog checkpointing on an existing stream and maintain the state information stored in the checkpoint.

Important

Queries that have enabled changelog checkpointing can only be run on Databricks Runtime 13.3 LTS and above. You can disable changelog checkpointing to revert to legacy checkpointing behavior, but you must continue to run these queries on Databricks Runtime 13.3 LTS or above. You must restart the job for these changes to take place.

RocksDB state store metrics

Each state operator collects metrics related to the state management operations performed on its RocksDB instance to observe the state store and potentially help in debugging job slowness. These metrics are aggregated (sum) per state operator in job across all tasks where the state operator is running. These metrics are part of the customMetrics map inside the stateOperators fields in StreamingQueryProgress. The following is an example of StreamingQueryProgress in JSON form (obtained using StreamingQueryProgress.json()).

{
  "id" : "6774075e-8869-454b-ad51-513be86cfd43",
  "runId" : "3d08104d-d1d4-4d1a-b21e-0b2e1fb871c5",
  "batchId" : 7,
  "stateOperators" : [ {
    "numRowsTotal" : 20000000,
    "numRowsUpdated" : 20000000,
    "memoryUsedBytes" : 31005397,
    "numRowsDroppedByWatermark" : 0,
    "customMetrics" : {
      "rocksdbBytesCopied" : 141037747,
      "rocksdbCommitCheckpointLatency" : 2,
      "rocksdbCommitCompactLatency" : 22061,
      "rocksdbCommitFileSyncLatencyMs" : 1710,
      "rocksdbCommitFlushLatency" : 19032,
      "rocksdbCommitPauseLatency" : 0,
      "rocksdbCommitWriteBatchLatency" : 56155,
      "rocksdbFilesCopied" : 2,
      "rocksdbFilesReused" : 0,
      "rocksdbGetCount" : 40000000,
      "rocksdbGetLatency" : 21834,
      "rocksdbPutCount" : 1,
      "rocksdbPutLatency" : 56155599000,
      "rocksdbReadBlockCacheHitCount" : 1988,
      "rocksdbReadBlockCacheMissCount" : 40341617,
      "rocksdbSstFileSize" : 141037747,
      "rocksdbTotalBytesReadByCompaction" : 336853375,
      "rocksdbTotalBytesReadByGet" : 680000000,
      "rocksdbTotalBytesReadThroughIterator" : 0,
      "rocksdbTotalBytesWrittenByCompaction" : 141037747,
      "rocksdbTotalBytesWrittenByPut" : 740000012,
      "rocksdbTotalCompactionLatencyMs" : 21949695000,
      "rocksdbWriterStallLatencyMs" : 0,
      "rocksdbZipFileBytesUncompressed" : 7038
    }
  } ],
  "sources" : [ {
  } ],
  "sink" : {
  }
}

Detailed descriptions of the metrics are as follows:

Metric name Description
rocksdbCommitWriteBatchLatency Time (in millis) took for applying the staged writes in in-memory structure (WriteBatch) to native RocksDB.
rocksdbCommitFlushLatency Time (in millis) took for flushing the RocksDB in-memory changes to local disk.
rocksdbCommitCompactLatency Time (in millis) took for compaction (optional) during the checkpoint commit.
rocksdbCommitPauseLatency Time (in millis) took for stopping the background worker threads (for compaction etc.) as part of the checkpoint commit.
rocksdbCommitCheckpointLatency Time (in millis) took for taking a snapshot of native RocksDB and write it to a local directory.
rocksdbCommitFileSyncLatencyMs Time (in millis) took for syncing the native RocksDB snapshot related files to an external storage (checkpoint location).
rocksdbGetLatency Average time (in nanos) took per the underlying native RocksDB::Get call.
rocksdbPutCount Average time (in nanos) took per the underlying native RocksDB::Put call.
rocksdbGetCount Number of native RocksDB::Get calls (doesn't include Gets from WriteBatch - in memory batch used for staging writes).
rocksdbPutCount Number of native RocksDB::Put calls (doesn't include Puts to WriteBatch - in memory batch used for staging writes).
rocksdbTotalBytesReadByGet Number of uncompressed bytes read through native RocksDB::Get calls.
rocksdbTotalBytesWrittenByPut Number of uncompressed bytes written through native RocksDB::Put calls.
rocksdbReadBlockCacheHitCount Number of times the native RocksDB block cache is used to avoid reading data from local disk.
rocksdbReadBlockCacheMissCount Number of times the native RocksDB block cache missed and required reading data from local disk.
rocksdbTotalBytesReadByCompaction Number of bytes read from the local disk by the native RocksDB compaction process.
rocksdbTotalBytesWrittenByCompaction Number of bytes written to the local disk by the native RocksDB compaction process.
rocksdbTotalCompactionLatencyMs Time (in millis) took for RocksDB compactions (both background and the optional compaction initiated during the commit).
rocksdbWriterStallLatencyMs Time (in millis) the writer has stalled due to a background compaction or flushing of the memtables to disk.
rocksdbTotalBytesReadThroughIterator Some of the stateful operations (such as timeout processing in flatMapGroupsWithState or watermarking in windowed aggregations) requires reading entire data in DB through iterator. The total size of uncompressed data read using the iterator.