system.events

Querying in ClickHouse Cloud

The data in this system table is held locally on each node in ClickHouse Cloud. Obtaining a complete view of all data, therefore, requires the clusterAllReplicas function. See here for further details.

Contains information about the number of events that have occurred in the system. For example, in the table, you can find how many SELECT queries were processed since the ClickHouse server started.

Columns:

• event (String) — Event name.
• value (UInt64) — Number of events occurred.
• description (String) — Event description.

OSS

The following events are available in ClickHouse OSS:

Event	Description
Query	Number of queries to be interpreted and potentially executed. Does not include queries that failed to parse or were rejected due to AST size limits, quota limits or limits on the number of simultaneously running queries. May include internal queries initiated by ClickHouse itself. Does not count subqueries.
SelectQuery	Same as Query, but only for SELECT queries.
InitialQuery	Same as Query, but only counts initial queries (see is_initial_query).
InitialSelectQuery	Same as InitialQuery, but only for SELECT queries.
QueriesWithSubqueries	Count queries with all subqueries
SelectQueriesWithSubqueries	Count SELECT queries with all subqueries
FileOpen	Number of files opened.
Seek	Number of times the 'lseek' function was called.
ReadBufferFromFileDescriptorRead	Number of reads (read/pread) from a file descriptor. Does not include sockets.
ReadBufferFromFileDescriptorReadBytes	Number of bytes read from file descriptors. If the file is compressed, this will show the compressed data size.
WriteBufferFromFileDescriptorWrite	Number of writes (write/pwrite) to a file descriptor. Does not include sockets.
WriteBufferFromFileDescriptorWriteBytes	Number of bytes written to file descriptors. If the file is compressed, this will show compressed data size.
FileSync	Number of times the F_FULLFSYNC/fsync/fdatasync function was called for files.
FileSyncElapsedMicroseconds	Total time spent waiting for F_FULLFSYNC/fsync/fdatasync syscall for files.
IOBufferAllocs	Number of allocations of IO buffers (for ReadBuffer/WriteBuffer).
IOBufferAllocBytes	Number of bytes allocated for IO buffers (for ReadBuffer/WriteBuffer).
DiskReadElapsedMicroseconds	Total time spent waiting for read syscall. This include reads from page cache.
DiskWriteElapsedMicroseconds	Total time spent waiting for write syscall. This include writes to page cache.
NetworkReceiveElapsedMicroseconds	Total time spent waiting for data to receive or receiving data from network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
NetworkSendElapsedMicroseconds	Total time spent waiting for data to send to network or sending data to network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
NetworkReceiveBytes	Total number of bytes received from network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
NetworkSendBytes	Total number of bytes send to network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
GlobalThreadPoolExpansions	Counts the total number of times new threads have been added to the global thread pool. This metric indicates the frequency of expansions in the global thread pool to accommodate increased processing demands.
GlobalThreadPoolThreadCreationMicroseconds	Total time spent waiting for new threads to start.
GlobalThreadPoolLockWaitMicroseconds	Total time threads have spent waiting for locks in the global thread pool.
GlobalThreadPoolJobs	Counts the number of jobs that have been pushed to the global thread pool.
GlobalThreadPoolJobWaitTimeMicroseconds	Measures the elapsed time from when a job is scheduled in the thread pool to when it is picked up for execution by a worker thread. This metric helps identify delays in job processing, indicating the responsiveness of the thread pool to new tasks.
LocalThreadPoolExpansions	Counts the total number of times threads have been borrowed from the global thread pool to expand local thread pools.
LocalThreadPoolShrinks	Counts the total number of times threads have been returned to the global thread pool from local thread pools.
LocalThreadPoolThreadCreationMicroseconds	Total time local thread pools have spent waiting to borrow a thread from the global pool.
LocalThreadPoolJobs	Counts the number of jobs that have been pushed to the local thread pools.
LocalThreadPoolBusyMicroseconds	Total time threads have spent executing the actual work.
LocalThreadPoolJobWaitTimeMicroseconds	Measures the elapsed time from when a job is scheduled in the thread pool to when it is picked up for execution by a worker thread. This metric helps identify delays in job processing, indicating the responsiveness of the thread pool to new tasks.
QueryPlanOptimizeMicroseconds	Total time spent executing query plan optimizations.
ContextLock	Number of times the lock of Context was acquired or tried to acquire. This is global lock.
RWLockAcquiredReadLocks	Number of times a read lock was acquired (in a heavy RWLock).
QueryProfilerSignalOverruns	Number of times we drop processing of a query profiler signal due to overrun plus the number of signals that OS has not delivered due to overrun.
QueryProfilerRuns	Number of times QueryProfiler had been run.
MainConfigLoads	Number of times the main configuration was reloaded.
ServerStartupMilliseconds	Time elapsed from starting server to listening to sockets in milliseconds
AsyncLoaderWaitMicroseconds	Total time a query was waiting for async loader jobs.
LogTrace	Number of log messages with level Trace
LogDebug	Number of log messages with level Debug
LogInfo	Number of log messages with level Info
LogWarning	Number of log messages with level Warning
LoggerElapsedNanoseconds	Cumulative time spend in logging
InterfaceNativeSendBytes	Number of bytes sent through native interfaces
InterfaceNativeReceiveBytes	Number of bytes received through native interfaces
MemoryWorkerRun	Number of runs done by MemoryWorker in background
MemoryWorkerRunElapsedMicroseconds	Total time spent by MemoryWorker for background work
AsyncLoggingFileLogTotalMessages	How many messages (accepted or dropped) have been sent to the async queue for the file log
AsyncLoggingErrorFileLogTotalMessages	How many messages (accepted or dropped) have been sent to the async queue for the error file log
AsyncLoggingTextLogTotalMessages	How many messages (accepted or dropped) have been sent to the async queue for the text_log

You can find all supported events in source file src/Common/ProfileEvents.cpp.

Cloud

The following events are available in ClickHouse Cloud:

Event	Description
Query	Number of queries to be interpreted and potentially executed. Does not include queries that failed to parse or were rejected due to AST size limits, quota limits or limits on the number of simultaneously running queries. May include internal queries initiated by ClickHouse itself. Does not count subqueries.
SelectQuery	Same as Query, but only for SELECT queries.
InitialQuery	Same as Query, but only counts initial queries (see is_initial_query).
QueriesWithSubqueries	Count queries with all subqueries
SelectQueriesWithSubqueries	Count SELECT queries with all subqueries
SelectQueriesWithPrimaryKeyUsage	Count SELECT queries which use the primary key to evaluate the WHERE condition
QueryTimeMicroseconds	Total time of all queries.
SelectQueryTimeMicroseconds	Total time of SELECT queries.
OtherQueryTimeMicroseconds	Total time of queries that are not SELECT or INSERT.
FileOpen	Number of files opened.
Seek	Number of times the 'lseek' function was called.
ReadBufferFromFileDescriptorRead	Number of reads (read/pread) from a file descriptor. Does not include sockets.
ReadBufferFromFileDescriptorReadBytes	Number of bytes read from file descriptors. If the file is compressed, this will show the compressed data size.
WriteBufferFromFileDescriptorWrite	Number of writes (write/pwrite) to a file descriptor. Does not include sockets.
WriteBufferFromFileDescriptorWriteBytes	Number of bytes written to file descriptors. If the file is compressed, this will show compressed data size.
ReadCompressedBytes	Number of bytes (the number of bytes before decompression) read from compressed sources (files, network).
CompressedReadBufferBlocks	Number of compressed blocks (the blocks of data that are compressed independent of each other) read from compressed sources (files, network).
CompressedReadBufferBytes	Number of uncompressed bytes (the number of bytes after decompression) read from compressed sources (files, network).
OpenedFileCacheHits	Number of times a file has been found in the opened file cache, so we didn't have to open it again.
OpenedFileCacheMisses	Number of times a file has been found in the opened file cache, so we had to open it again.
OpenedFileCacheMicroseconds	Amount of time spent executing OpenedFileCache methods.
IOBufferAllocs	Number of allocations of IO buffers (for ReadBuffer/WriteBuffer).
IOBufferAllocBytes	Number of bytes allocated for IO buffers (for ReadBuffer/WriteBuffer).
ArenaAllocChunks	Number of chunks allocated for memory Arena (used for GROUP BY and similar operations)
ArenaAllocBytes	Number of bytes allocated for memory Arena (used for GROUP BY and similar operations)
FunctionExecute	Number of SQL ordinary function calls (SQL functions are called on per-block basis, so this number represents the number of blocks).
TableFunctionExecute	Number of table function calls.
DefaultImplementationForNullsRows	Number of rows processed by default implementation for nulls in function execution
DefaultImplementationForNullsRowsWithNulls	Number of rows which contain null values processed by default implementation for nulls in function execution
MarkCacheHits	Number of times an entry has been found in the mark cache, so we didn't have to load a mark file.
MarkCacheMisses	Number of times an entry has not been found in the mark cache, so we had to load a mark file in memory, which is a costly operation, adding to query latency.
QueryConditionCacheHits	Number of times an entry has been found in the query condition cache (and reading of marks can be skipped). Only updated for SELECT queries with SETTING use_query_condition_cache = 1.
QueryConditionCacheMisses	Number of times an entry has not been found in the query condition cache (and reading of mark cannot be skipped). Only updated for SELECT queries with SETTING use_query_condition_cache = 1.
CreatedReadBufferOrdinary	Number of times ordinary read buffer was created for reading data (while choosing among other read methods).
DiskReadElapsedMicroseconds	Total time spent waiting for read syscall. This include reads from page cache.
DiskWriteElapsedMicroseconds	Total time spent waiting for write syscall. This include writes to page cache.
NetworkReceiveElapsedMicroseconds	Total time spent waiting for data to receive or receiving data from network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
NetworkSendElapsedMicroseconds	Total time spent waiting for data to send to network or sending data to network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
NetworkReceiveBytes	Total number of bytes received from network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
NetworkSendBytes	Total number of bytes send to network. Only ClickHouse-related network interaction is included, not by 3rd party libraries.
GlobalThreadPoolExpansions	Counts the total number of times new threads have been added to the global thread pool. This metric indicates the frequency of expansions in the global thread pool to accommodate increased processing demands.
GlobalThreadPoolThreadCreationMicroseconds	Total time spent waiting for new threads to start.
GlobalThreadPoolLockWaitMicroseconds	Total time threads have spent waiting for locks in the global thread pool.
GlobalThreadPoolJobs	Counts the number of jobs that have been pushed to the global thread pool.
GlobalThreadPoolJobWaitTimeMicroseconds	Measures the elapsed time from when a job is scheduled in the thread pool to when it is picked up for execution by a worker thread. This metric helps identify delays in job processing, indicating the responsiveness of the thread pool to new tasks.
LocalThreadPoolExpansions	Counts the total number of times threads have been borrowed from the global thread pool to expand local thread pools.
LocalThreadPoolShrinks	Counts the total number of times threads have been returned to the global thread pool from local thread pools.
LocalThreadPoolThreadCreationMicroseconds	Total time local thread pools have spent waiting to borrow a thread from the global pool.
LocalThreadPoolLockWaitMicroseconds	Total time threads have spent waiting for locks in the local thread pools.
LocalThreadPoolJobs	Counts the number of jobs that have been pushed to the local thread pools.
LocalThreadPoolBusyMicroseconds	Total time threads have spent executing the actual work.
LocalThreadPoolJobWaitTimeMicroseconds	Measures the elapsed time from when a job is scheduled in the thread pool to when it is picked up for execution by a worker thread. This metric helps identify delays in job processing, indicating the responsiveness of the thread pool to new tasks.
RemoteReadThrottlerBytes	Bytes passed through 'max_remote_read_network_bandwidth_for_server'/'max_remote_read_network_bandwidth' throttler.
RemoteWriteThrottlerBytes	Bytes passed through 'max_remote_write_network_bandwidth_for_server'/'max_remote_write_network_bandwidth' throttler.
InsertedRows	Number of rows INSERTed to all tables.
InsertedBytes	Number of bytes (uncompressed; for columns as they stored in memory) INSERTed to all tables.
ZooKeeperInit	Number of times connection with ZooKeeper has been established.
ZooKeeperTransactions	Number of ZooKeeper operations, which include both read and write operations as well as multi-transactions.
ZooKeeperList	Number of 'list' (getChildren) requests to ZooKeeper.
ZooKeeperCreate	Number of 'create' requests to ZooKeeper.
ZooKeeperRemove	Number of 'remove' requests to ZooKeeper.
ZooKeeperExists	Number of 'exists' requests to ZooKeeper.
ZooKeeperGet	Number of 'get' requests to ZooKeeper.
ZooKeeperSet	Number of 'set' requests to ZooKeeper.
ZooKeeperMulti	Number of 'multi' requests to ZooKeeper (compound transactions).
ZooKeeperMultiRead	Number of read 'multi' requests to ZooKeeper (compound transactions).
ZooKeeperMultiWrite	Number of write 'multi' requests to ZooKeeper (compound transactions).
ZooKeeperSync	Number of 'sync' requests to ZooKeeper. These requests are rarely needed or usable.
ZooKeeperClose	Number of times connection with ZooKeeper has been closed voluntary.
ZooKeeperWatchResponse	Number of times watch notification has been received from ZooKeeper.
ZooKeeperWaitMicroseconds	Number of microseconds spent waiting for responses from ZooKeeper after creating a request, summed across all the requesting threads.
ZooKeeperBytesSent	Number of bytes send over network while communicating with ZooKeeper.
ZooKeeperBytesReceived	Number of bytes received over network while communicating with ZooKeeper.
DistributedConnectionTries	Total count of distributed connection attempts.
DistributedConnectionUsable	Total count of successful distributed connections to a usable server (with required table, but maybe stale).
SuspendSendingQueryToShard	Total count when sending query to shard was suspended when async_query_sending_for_remote is enabled.
CompileFunction	Number of times a compilation of generated LLVM code (to create fused function for complex expressions) was initiated.
CompileExpressionsMicroseconds	Total time spent for compilation of expressions to LLVM code.
CompileExpressionsBytes	Number of bytes used for expressions compilation.
QueryPlanOptimizeMicroseconds	Total time spent executing query plan optimizations.
SelectedParts	Number of data parts selected to read from a MergeTree table.
SelectedPartsTotal	Number of total data parts before selecting which ones to read from a MergeTree table.
SelectedRanges	Number of (non-adjacent) ranges in all data parts selected to read from a MergeTree table.
SelectedMarks	Number of marks (index granules) selected to read from a MergeTree table.
SelectedMarksTotal	Number of total marks (index granules) before selecting which ones to read from a MergeTree table.
SelectedRows	Number of rows SELECTed from all tables.
SelectedBytes	Number of bytes (uncompressed; for columns as they stored in memory) SELECTed from all tables.
RowsReadByMainReader	Number of rows read from MergeTree tables by the main reader (after PREWHERE step).
RowsReadByPrewhereReaders	Number of rows read from MergeTree tables (in total) by prewhere readers.
LoadedDataParts	Number of data parts loaded by MergeTree tables during initialization.
LoadedDataPartsMicroseconds	Microseconds spent by MergeTree tables for loading data parts during initialization.
FilteringMarksWithPrimaryKeyMicroseconds	Time spent filtering parts by PK.
WaitMarksLoadMicroseconds	Time spent loading marks
BackgroundLoadingMarksTasks	Number of background tasks for loading marks
MarksTasksFromCache	Number of times marks were loaded synchronously because they were already present in the cache.
LoadedMarksFiles	Number of mark files loaded.
LoadedMarksCount	Number of marks loaded (total across columns).
LoadedMarksMemoryBytes	Size of in-memory representations of loaded marks.
LoadedPrimaryIndexFiles	Number of primary index files loaded.
LoadedPrimaryIndexRows	Number of rows of primary key loaded.
LoadedPrimaryIndexBytes	Number of rows of primary key loaded.
Merge	Number of launched background merges.
MergeSourceParts	Number of source parts scheduled for merges.
MergedRows	Rows read for background merges. This is the number of rows before merge.
MergedColumns	Number of columns merged during the horizontal stage of merges.
MergedUncompressedBytes	Uncompressed bytes (for columns as they stored in memory) that was read for background merges. This is the number before merge.
MergeTotalMilliseconds	Total time spent for background merges
MergeExecuteMilliseconds	Total busy time spent for execution of background merges
MergeHorizontalStageTotalMilliseconds	Total time spent for horizontal stage of background merges
MergeHorizontalStageExecuteMilliseconds	Total busy time spent for execution of horizontal stage of background merges
MergeVerticalStageTotalMilliseconds	Total time spent for vertical stage of background merges
MergeProjectionStageTotalMilliseconds	Total time spent for projection stage of background merges
MergeProjectionStageExecuteMilliseconds	Total busy time spent for execution of projection stage of background merges
MergePrewarmStageTotalMilliseconds	Total time spent for prewarm stage of background merges
MergePrewarmStageExecuteMilliseconds	Total busy time spent for execution of prewarm stage of background merges
MergeTreeDataWriterRows	Number of rows INSERTed to MergeTree tables.
MergeTreeDataWriterUncompressedBytes	Uncompressed bytes (for columns as they stored in memory) INSERTed to MergeTree tables.
MergeTreeDataWriterCompressedBytes	Bytes written to filesystem for data INSERTed to MergeTree tables.
MergeTreeDataWriterBlocks	Number of blocks INSERTed to MergeTree tables. Each block forms a data part of level zero.
MergeTreeDataWriterBlocksAlreadySorted	Number of blocks INSERTed to MergeTree tables that appeared to be already sorted.
MergeMutateBackgroundExecutorTaskExecuteStepMicroseconds	Time spent in executeStep() for MergeMutate executor tasks.
MergeMutateBackgroundExecutorTaskResetMicroseconds	Time spent resetting task for MergeMutate executor.
CommonBackgroundExecutorTaskExecuteStepMicroseconds	Time spent in executeStep() for Common executor tasks.
CommonBackgroundExecutorTaskResetMicroseconds	Time spent resetting task for Common executor.
MergeTreeDataWriterSortingBlocksMicroseconds	Time spent sorting blocks
InsertedCompactParts	Number of parts inserted in Compact format.
MergedIntoCompactParts	Number of parts merged into Compact format.
RegexpWithMultipleNeedlesCreated	Regular expressions with multiple needles (VectorScan library) compiled.
RegexpWithMultipleNeedlesGlobalCacheHit	Number of times we fetched compiled regular expression with multiple needles (VectorScan library) from the global cache.
RegexpWithMultipleNeedlesGlobalCacheMiss	Number of times we failed to fetch compiled regular expression with multiple needles (VectorScan library) from the global cache.
ContextLock	Number of times the lock of Context was acquired or tried to acquire. This is global lock.
ContextLockWaitMicroseconds	Context lock wait time in microseconds
RWLockAcquiredReadLocks	Number of times a read lock was acquired (in a heavy RWLock).
PartsLockHoldMicroseconds	Total time spent holding data parts lock in MergeTree tables
PartsLockWaitMicroseconds	Total time spent waiting for data parts lock in MergeTree tables
RealTimeMicroseconds	Total (wall clock) time spent in processing (queries and other tasks) threads (note that this is a sum).
UserTimeMicroseconds	Total time spent in processing (queries and other tasks) threads executing CPU instructions in user mode. This includes time CPU pipeline was stalled due to main memory access, cache misses, branch mispredictions, hyper-threading, etc.
SystemTimeMicroseconds	Total time spent in processing (queries and other tasks) threads executing CPU instructions in OS kernel mode. This is time spent in syscalls, excluding waiting time during blocking syscalls.
MemoryAllocatorPurge	Total number of times memory allocator purge was requested
MemoryAllocatorPurgeTimeMicroseconds	Total time spent for memory allocator purge
SoftPageFaults	The number of soft page faults in query execution threads. Soft page fault usually means a miss in the memory allocator cache, which requires a new memory mapping from the OS and subsequent allocation of a page of physical memory.
OSCPUWaitMicroseconds	Total time a thread was ready for execution but waiting to be scheduled by OS, from the OS point of view.
OSCPUVirtualTimeMicroseconds	CPU time spent seen by OS. Does not include involuntary waits due to virtualization.
OSWriteBytes	Number of bytes written to disks or block devices. Doesn't include bytes that are in page cache dirty pages. May not include data that was written by OS asynchronously.
OSReadChars	Number of bytes read from filesystem, including page cache.
OSWriteChars	Number of bytes written to filesystem, including page cache.
QueryProfilerRuns	Number of times QueryProfiler had been run.
S3ReadMicroseconds	Time of GET and HEAD requests to S3 storage.
S3ReadRequestsCount	Number of GET and HEAD requests to S3 storage.
S3ReadRequestsErrors	Number of non-throttling errors in GET and HEAD requests to S3 storage.
S3ReadRequestAttempts	Number of attempts for GET and HEAD requests, including the initial try and any retries, but excluding retries performed internally by the S3 retry strategy
S3WriteMicroseconds	Time of POST, DELETE, PUT and PATCH requests to S3 storage.
S3WriteRequestsCount	Number of POST, DELETE, PUT and PATCH requests to S3 storage.
S3WriteRequestAttempts	Number of attempts for POST, DELETE, PUT and PATCH requests, including the initial try and any retries, but excluding retries performed internally by the retry strategy
DiskS3ReadMicroseconds	Time of GET and HEAD requests to DiskS3 storage.
DiskS3ReadRequestsCount	Number of GET and HEAD requests to DiskS3 storage.
DiskS3ReadRequestsErrors	Number of non-throttling errors in GET and HEAD requests to DiskS3 storage.
DiskS3ReadRequestAttempts	Number of attempts for GET and HEAD requests to DiskS3 storage, including the initial try and any retries, but excluding retries performed internally by the S3 retry strategy
DiskS3WriteMicroseconds	Time of POST, DELETE, PUT and PATCH requests to DiskS3 storage.
DiskS3WriteRequestsCount	Number of POST, DELETE, PUT and PATCH requests to DiskS3 storage.
DiskS3WriteRequestAttempts	Number of attempts for POST, DELETE, PUT and PATCH requests to DiskS3 storage, including the initial try and any retries, but excluding retries performed internally by the retry strategy
S3DeleteObjects	Number of S3 API DeleteObject(s) calls.
S3ListObjects	Number of S3 API ListObjects calls.
S3HeadObject	Number of S3 API HeadObject calls.
S3PutObject	Number of S3 API PutObject calls.
S3GetObject	Number of S3 API GetObject calls.
DiskS3DeleteObjects	Number of DiskS3 API DeleteObject(s) calls.
DiskS3ListObjects	Number of DiskS3 API ListObjects calls.
DiskS3HeadObject	Number of DiskS3 API HeadObject calls.
DiskS3PutObject	Number of DiskS3 API PutObject calls.
DiskS3GetObject	Number of DiskS3 API GetObject calls.
DiskPlainRewritableS3DirectoryCreated	Number of directories created by the 'plain_rewritable' metadata storage for S3ObjectStorage.
DiskPlainRewritableS3DirectoryRemoved	Number of directories removed by the 'plain_rewritable' metadata storage for S3ObjectStorage.
S3Clients	Number of created S3 clients.
ReadBufferFromS3Microseconds	Time spent on reading from S3.
ReadBufferFromS3InitMicroseconds	Time spent initializing connection to S3.
ReadBufferFromS3Bytes	Bytes read from S3.
WriteBufferFromS3Microseconds	Time spent on writing to S3.
WriteBufferFromS3Bytes	Bytes written to S3.
CachedReadBufferReadFromCacheHits	Number of times the read from filesystem cache hit the cache.
CachedReadBufferReadFromCacheMisses	Number of times the read from filesystem cache miss the cache.
CachedReadBufferReadFromSourceMicroseconds	Time reading from filesystem cache source (from remote filesystem, etc)
CachedReadBufferReadFromCacheMicroseconds	Time reading from filesystem cache
CachedReadBufferReadFromSourceBytes	Bytes read from filesystem cache source (from remote fs, etc)
CachedReadBufferReadFromCacheBytes	Bytes read from filesystem cache
CachedReadBufferCacheWriteBytes	Bytes written from source (remote fs, etc) to filesystem cache
CachedReadBufferCacheWriteMicroseconds	Time spent writing data into filesystem cache
CachedReadBufferCreateBufferMicroseconds	Prepare buffer time
CachedWriteBufferCacheWriteBytes	Bytes written from source (remote fs, etc) to filesystem cache
CachedWriteBufferCacheWriteMicroseconds	Time spent writing data into filesystem cache
FilesystemCacheLoadMetadataMicroseconds	Time spent loading filesystem cache metadata
FilesystemCacheCreatedKeyDirectories	Number of created key directories
FilesystemCacheBackgroundDownloadQueuePush	Number of file segments sent for background download in filesystem cache
FilesystemCacheLockKeyMicroseconds	Lock cache key time
FilesystemCacheLockMetadataMicroseconds	Lock filesystem cache metadata time
FilesystemCacheLockCacheMicroseconds	Lock filesystem cache time
FilesystemCacheReserveMicroseconds	Filesystem cache space reservation time
FilesystemCacheReserveAttempts	Filesystem cache space reservation attempt
FilesystemCacheGetOrSetMicroseconds	Filesystem cache getOrSet() time
FilesystemCacheGetMicroseconds	Filesystem cache get() time
FileSegmentCompleteMicroseconds	Duration of FileSegment::complete() in filesystem cache
FileSegmentLockMicroseconds	Lock file segment time
FileSegmentWriteMicroseconds	File segment write() time
FileSegmentUseMicroseconds	File segment use() time
FileSegmentHolderCompleteMicroseconds	File segments holder complete() time
FileSegmentFailToIncreasePriority	Number of times the priority was not increased due to a high contention on the cache lock
FilesystemCacheHoldFileSegments	Filesystem cache file segments count, which were hold
FilesystemCacheUnusedHoldFileSegments	Filesystem cache file segments count, which were hold, but not used (because of seek or LIMIT n, etc)
RemoteFSSeeks	Total number of seeks for async buffer
RemoteFSPrefetches	Number of prefetches made with asynchronous reading from remote filesystem
RemoteFSCancelledPrefetches	Number of cancelled prefecthes (because of seek)
RemoteFSUnusedPrefetches	Number of prefetches pending at buffer destruction
RemoteFSPrefetchedReads	Number of reads from prefecthed buffer
RemoteFSPrefetchedBytes	Number of bytes from prefecthed buffer
RemoteFSUnprefetchedReads	Number of reads from unprefetched buffer
RemoteFSUnprefetchedBytes	Number of bytes from unprefetched buffer
RemoteFSBuffers	Number of buffers created for asynchronous reading from remote filesystem
WaitPrefetchTaskMicroseconds	Time spend waiting for prefetched reader
ThreadpoolReaderTaskMicroseconds	Time spent getting the data in asynchronous reading
ThreadpoolReaderReadBytes	Bytes read from a threadpool task in asynchronous reading
ThreadpoolReaderSubmit	Bytes read from a threadpool task in asynchronous reading
ThreadpoolReaderSubmitReadSynchronously	How many times we haven't scheduled a task on the thread pool and read synchronously instead
ThreadpoolReaderSubmitReadSynchronouslyBytes	How many bytes were read synchronously
ThreadpoolReaderSubmitReadSynchronouslyMicroseconds	How much time we spent reading synchronously
ThreadpoolReaderSubmitLookupInCacheMicroseconds	How much time we spent checking if content is cached
FileSegmentWaitReadBufferMicroseconds	Metric per file segment. Time spend waiting for internal read buffer (includes cache waiting)
FileSegmentReadMicroseconds	Metric per file segment. Time spend reading from file
FileSegmentCacheWriteMicroseconds	Metric per file segment. Time spend writing data to cache
FileSegmentUsedBytes	Metric per file segment. How many bytes were actually used from current file segment
ThreadPoolReaderPageCacheMiss	Number of times the read inside ThreadPoolReader was not done from page cache and was hand off to thread pool.
ThreadPoolReaderPageCacheMissBytes	Number of bytes read inside ThreadPoolReader when read was not done from page cache and was hand off to thread pool.
ThreadPoolReaderPageCacheMissElapsedMicroseconds	Time spent reading data inside the asynchronous job in ThreadPoolReader - when read was not done from the page cache.
SynchronousReadWaitMicroseconds	Time spent in waiting for synchronous reads in asynchronous local read.
AsynchronousRemoteReadWaitMicroseconds	Time spent in waiting for asynchronous remote reads.
SynchronousRemoteReadWaitMicroseconds	Time spent in waiting for synchronous remote reads.
MainConfigLoads	Number of times the main configuration was reloaded.
MetadataFromKeeperCacheHit	Number of times an object storage metadata request was answered from cache without making request to Keeper
MetadataFromKeeperCacheMiss	Number of times an object storage metadata request had to be answered from Keeper
MetadataFromKeeperCacheUpdateMicroseconds	Total time spent in updating the cache including waiting for responses from Keeper
MetadataFromKeeperUpdateCacheOneLevel	Number of times a cache update for one level of directory tree was done
MetadataFromKeeperTransactionCommit	Number of times metadata transaction commit was attempted
MetadataFromKeeperCleanupTransactionCommit	Number of times metadata transaction commit for deleted objects cleanup was attempted
MetadataFromKeeperOperations	Number of times a request was made to Keeper
MetadataFromKeeperIndividualOperations	Number of paths read or written by single or multi requests to Keeper
MetadataFromKeeperIndividualOperationsMicroseconds	Time spend during single or multi requests to Keeper
SharedMergeTreeMetadataCacheHintLoadedFromCache	Number of times metadata cache hint was found without going to Keeper
ScalarSubqueriesCacheMiss	Number of times a read from a scalar subquery was not cached and had to be calculated completely
ServerStartupMilliseconds	Time elapsed from starting server to listening to sockets in milliseconds
MergerMutatorsGetPartsForMergeElapsedMicroseconds	Time spent to take data parts snapshot to build ranges from them.
MergerMutatorPrepareRangesForMergeElapsedMicroseconds	Time spent to prepare parts ranges which can be merged according to merge predicate.
MergerMutatorSelectPartsForMergeElapsedMicroseconds	Time spent to select parts from ranges which can be merged.
MergerMutatorRangesForMergeCount	Amount of candidate ranges for merge
MergerMutatorPartsInRangesForMergeCount	Amount of candidate parts for merge
MergerMutatorSelectRangePartsCount	Amount of parts in selected range for merge
AsyncLoaderWaitMicroseconds	Total time a query was waiting for async loader jobs.
LogTrace	Number of log messages with level Trace
LogDebug	Number of log messages with level Debug
LogInfo	Number of log messages with level Info
LogWarning	Number of log messages with level Warning
LogError	Number of log messages with level Error
LoggerElapsedNanoseconds	Cumulative time spend in logging
InterfaceHTTPSendBytes	Number of bytes sent through HTTP interfaces
InterfaceHTTPReceiveBytes	Number of bytes received through HTTP interfaces
InterfaceNativeSendBytes	Number of bytes sent through native interfaces
InterfaceNativeReceiveBytes	Number of bytes received through native interfaces
InterfacePrometheusSendBytes	Number of bytes sent through Prometheus interfaces
InterfacePrometheusReceiveBytes	Number of bytes received through Prometheus interfaces
InterfaceInterserverSendBytes	Number of bytes sent through interserver interfaces
InterfaceInterserverReceiveBytes	Number of bytes received through interserver interfaces
SharedMergeTreeVirtualPartsUpdates	Virtual parts update count
SharedMergeTreeVirtualPartsUpdatesByLeader	Virtual parts updates by leader
SharedMergeTreeVirtualPartsUpdateMicroseconds	Virtual parts update microseconds
SharedMergeTreeVirtualPartsUpdatesFromZooKeeper	Virtual parts updates count from ZooKeeper
SharedMergeTreeVirtualPartsUpdatesFromZooKeeperMicroseconds	Virtual parts updates from ZooKeeper microseconds
SharedMergeTreeVirtualPartsUpdatesPeerNotFound	Virtual updates from peer failed because no one found
SharedMergeTreeVirtualPartsUpdatesLeaderSuccessfulElection	Virtual parts updates leader election successful
SharedMergeTreeMergeMutationAssignmentAttempt	How many times we tried to assign merge or mutation
SharedMergeTreeMergeMutationAssignmentFailedWithNothingToDo	How many times we tried to assign merge or mutation and failed because nothing to merge
SharedMergeTreePartsKillerRuns	How many times parts killer has been running
SharedMergeTreePartsKillerMicroseconds	How much time does parts killer main thread takes
SharedMergeTreeMergeSelectingTaskMicroseconds	Merge selecting task microseconds for SMT
SharedMergeTreeScheduleDataProcessingJob	How many times scheduleDataProcessingJob called/
SharedMergeTreeScheduleDataProcessingJobNothingToScheduled	How many times scheduleDataProcessingJob called but nothing to do
SharedMergeTreeScheduleDataProcessingJobMicroseconds	scheduleDataProcessingJob execute time
SharedMergeTreeHandleBlockingPartsMicroseconds	Time of handling blocking parts in scheduleDataProcessingJob
SharedMergeTreeHandleFetchPartsMicroseconds	Time of handling fetched parts in scheduleDataProcessingJob
SharedMergeTreeHandleOutdatedPartsMicroseconds	Time of handling outdated parts in scheduleDataProcessingJob
SharedMergeTreeTryUpdateDiskMetadataCacheForPartMicroseconds	Time of tryUpdateDiskMetadataCacheForPart in scheduleDataProcessingJob
DiskConnectionsCreated	Number of created connections for disk
DiskConnectionsReused	Number of reused connections for disk
DiskConnectionsReset	Number of reset connections for disk
DiskConnectionsPreserved	Number of preserved connections for disk
DiskConnectionsExpired	Number of expired connections for disk
DiskConnectionsElapsedMicroseconds	Total time spend on creating connections for disk
HTTPConnectionsCreated	Number of created client HTTP connections
HTTPConnectionsReused	Number of reused client HTTP connections
HTTPConnectionsPreserved	Number of preserved client HTTP connections
HTTPConnectionsElapsedMicroseconds	Total time spend on creating client HTTP connections
HTTPServerConnectionsCreated	Number of created server HTTP connections
HTTPServerConnectionsReused	Number of reused server HTTP connections
HTTPServerConnectionsPreserved	Number of preserved server HTTP connections. Connection kept alive successfully
HTTPServerConnectionsExpired	Number of expired server HTTP connections.
HTTPServerConnectionsReset	Number of reset server HTTP connections. Server closes connection
AddressesDiscovered	Total count of new addresses in DNS resolve results for HTTP connections
ReadWriteBufferFromHTTPRequestsSent	Number of HTTP requests sent by ReadWriteBufferFromHTTP
ReadWriteBufferFromHTTPBytes	Total size of payload bytes received and sent by ReadWriteBufferFromHTTP. Doesn't include HTTP headers.
ConcurrencyControlSlotsGranted	Number of CPU slot granted according to guarantee of 1 thread per query and for queries with setting 'use_concurrency_control' = 0
ConcurrencyControlSlotsAcquiredNonCompeting	Total number of noncompeting CPU slot acquired
MemoryWorkerRun	Number of runs done by MemoryWorker in background
MemoryWorkerRunElapsedMicroseconds	Total time spent by MemoryWorker for background work
FilterTransformPassedRows	Number of rows that passed the filter in the query
FilterTransformPassedBytes	Number of bytes that passed the filter in the query
IndexBinarySearchAlgorithm	Number of times the binary search algorithm is used over the index marks
IndexGenericExclusionSearchAlgorithm	Number of times the generic exclusion search algorithm is used over the index marks
AsyncLoggingConsoleTotalMessages	How many messages (accepted or dropped) have been sent to the async queue for the console log
AsyncLoggingFileLogTotalMessages	How many messages (accepted or dropped) have been sent to the async queue for the file log
AsyncLoggingErrorFileLogTotalMessages	How many messages (accepted or dropped) have been sent to the async queue for the error file log
AsyncLoggingTextLogTotalMessages	How many messages (accepted or dropped) have been sent to the async queue for the text_log

Example

SELECT * FROM system.events LIMIT 5

┌─event─────────────────────────────────┬─value─┬─description────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Query                                 │    12 │ Number of queries to be interpreted and potentially executed. Does not include queries that failed to parse or were rejected due to AST size limits, quota limits or limits on the number of simultaneously running queries. May include internal queries initiated by ClickHouse itself. Does not count subqueries.                  │
│ SelectQuery                           │     8 │ Same as Query, but only for SELECT queries.                                                                                                                                                                                                                │
│ FileOpen                              │    73 │ Number of files opened.                                                                                                                                                                                                                                    │
│ ReadBufferFromFileDescriptorRead      │   155 │ Number of reads (read/pread) from a file descriptor. Does not include sockets.                                                                                                                                                                             │
│ ReadBufferFromFileDescriptorReadBytes │  9931 │ Number of bytes read from file descriptors. If the file is compressed, this will show the compressed data size.                                                                                                                                              │
└───────────────────────────────────────┴───────┴────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

See Also

• system.asynchronous_metrics — Contains periodically calculated metrics.
• system.metrics — Contains instantly calculated metrics.
• system.metric_log — Contains a history of metrics values from tables system.metrics and system.events.
• Monitoring — Base concepts of ClickHouse monitoring.