perf_context.h

// Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).

#pragma once

#include <stdint.h>
#include <map>
#include <string>

#include "rocksdb/perf_level.h"

namespace ROCKSDB_NAMESPACE {

// A thread local context for gathering performance counter efficiently
// and transparently.
// Use SetPerfLevel(PerfLevel::kEnableTime) to enable time stats.

// Break down performance counters by level and store per-level perf context in
// PerfContextByLevel
struct PerfContextByLevel {
  // # of times bloom filter has avoided file reads, i.e., negatives.
  uint64_t bloom_filter_useful = 0;
  // # of times bloom FullFilter has not avoided the reads.
  uint64_t bloom_filter_full_positive = 0;
  // # of times bloom FullFilter has not avoided the reads and data actually
  // exist.
  uint64_t bloom_filter_full_true_positive = 0;

  // total number of user key returned (only include keys that are found, does
  // not include keys that are deleted or merged without a final put
  uint64_t user_key_return_count = 0;

  // total nanos spent on reading data from SST files
  uint64_t get_from_table_nanos = 0;

  uint64_t block_cache_hit_count = 0;   // total number of block cache hits
  uint64_t block_cache_miss_count = 0;  // total number of block cache misses

  void Reset();  // reset all performance counters to zero
};

struct PerfContext {
  ~PerfContext();

  PerfContext() {}

  PerfContext(const PerfContext&);
  PerfContext& operator=(const PerfContext&);
  PerfContext(PerfContext&&) noexcept;

  void Reset();  // reset all performance counters to zero

  std::string ToString(bool exclude_zero_counters = false) const;

  // enable per level perf context and allocate storage for PerfContextByLevel
  void EnablePerLevelPerfContext();

  // temporarily disable per level perf context by setting the flag to false
  void DisablePerLevelPerfContext();

  // free the space for PerfContextByLevel, also disable per level perf context
  void ClearPerLevelPerfContext();

  uint64_t user_key_comparison_count;  // total number of user key comparisons
  uint64_t block_cache_hit_count;      // total number of block cache hits
  uint64_t block_read_count;           // total number of block reads (with IO)
  uint64_t block_read_byte;            // total number of bytes from block reads
  uint64_t block_read_time;            // total nanos spent on block reads
  uint64_t block_cache_index_hit_count;   // total number of index block hits
  uint64_t index_block_read_count;        // total number of index block reads
  uint64_t block_cache_filter_hit_count;  // total number of filter block hits
  uint64_t filter_block_read_count;       // total number of filter block reads
  uint64_t compression_dict_block_read_count;  // total number of compression
                                               // dictionary block reads

  uint64_t secondary_cache_hit_count;  // total number of secondary cache hits

  uint64_t block_checksum_time;    // total nanos spent on block checksum
  uint64_t block_decompress_time;  // total nanos spent on block decompression

  uint64_t get_read_bytes;       // bytes for vals returned by Get
  uint64_t multiget_read_bytes;  // bytes for vals returned by MultiGet
  uint64_t iter_read_bytes;      // bytes for keys/vals decoded by iterator

  // total number of internal keys skipped over during iteration.
  // There are several reasons for it:
  // 1. when calling Next(), the iterator is in the position of the previous
  //    key, so that we'll need to skip it. It means this counter will always
  //    be incremented in Next().
  // 2. when calling Next(), we need to skip internal entries for the previous
  //    keys that are overwritten.
  // 3. when calling Next(), Seek() or SeekToFirst(), after previous key
  //    before calling Next(), the seek key in Seek() or the beginning for
  //    SeekToFirst(), there may be one or more deleted keys before the next
  //    valid key that the operation should place the iterator to. We need
  //    to skip both of the tombstone and updates hidden by the tombstones. The
  //    tombstones are not included in this counter, while previous updates
  //    hidden by the tombstones will be included here.
  // 4. symmetric cases for Prev() and SeekToLast()
  // internal_recent_skipped_count is not included in this counter.
  //
  uint64_t internal_key_skipped_count;
  // Total number of deletes and single deletes skipped over during iteration
  // When calling Next(), Seek() or SeekToFirst(), after previous position
  // before calling Next(), the seek key in Seek() or the beginning for
  // SeekToFirst(), there may be one or more deleted keys before the next valid
  // key. Every deleted key is counted once. We don't recount here if there are
  // still older updates invalidated by the tombstones.
  //
  uint64_t internal_delete_skipped_count;
  // How many times iterators skipped over internal keys that are more recent
  // than the snapshot that iterator is using.
  //
  uint64_t internal_recent_skipped_count;
  // How many values were fed into merge operator by iterators.
  //
  uint64_t internal_merge_count;

  uint64_t get_snapshot_time;        // total nanos spent on getting snapshot
  uint64_t get_from_memtable_time;   // total nanos spent on querying memtables
  uint64_t get_from_memtable_count;  // number of mem tables queried
  // total nanos spent after Get() finds a key
  uint64_t get_post_process_time;
  uint64_t get_from_output_files_time;  // total nanos reading from output files
  // total nanos spent on seeking memtable
  uint64_t seek_on_memtable_time;
  // number of seeks issued on memtable
  // (including SeekForPrev but not SeekToFirst and SeekToLast)
  uint64_t seek_on_memtable_count;
  // number of Next()s issued on memtable
  uint64_t next_on_memtable_count;
  // number of Prev()s issued on memtable
  uint64_t prev_on_memtable_count;
  // total nanos spent on seeking child iters
  uint64_t seek_child_seek_time;
  // number of seek issued in child iterators
  uint64_t seek_child_seek_count;
  uint64_t seek_min_heap_time;  // total nanos spent on the merge min heap
  uint64_t seek_max_heap_time;  // total nanos spent on the merge max heap
  // total nanos spent on seeking the internal entries
  uint64_t seek_internal_seek_time;
  // total nanos spent on iterating internal entries to find the next user entry
  uint64_t find_next_user_entry_time;

  // This group of stats provide a breakdown of time spent by Write().
  // May be inaccurate when 2PC, two_write_queues or enable_pipelined_write
  // are enabled.
  //
  // total nanos spent on writing to WAL
  uint64_t write_wal_time;
  // total nanos spent on writing to mem tables
  uint64_t write_memtable_time;
  // total nanos spent on delaying or throttling write
  uint64_t write_delay_time;
  // total nanos spent on switching memtable/wal and scheduling
  // flushes/compactions.
  uint64_t write_scheduling_flushes_compactions_time;
  // total nanos spent on writing a record, excluding the above four things
  uint64_t write_pre_and_post_process_time;

  // time spent waiting for other threads of the batch group
  uint64_t write_thread_wait_nanos;

  // time spent on acquiring DB mutex.
  uint64_t db_mutex_lock_nanos;
  // Time spent on waiting with a condition variable created with DB mutex.
  uint64_t db_condition_wait_nanos;
  // Time spent on merge operator.
  uint64_t merge_operator_time_nanos;

  // Time spent on reading index block from block cache or SST file
  uint64_t read_index_block_nanos;
  // Time spent on reading filter block from block cache or SST file
  uint64_t read_filter_block_nanos;
  // Time spent on creating data block iterator
  uint64_t new_table_block_iter_nanos;
  // Time spent on creating a iterator of an SST file.
  uint64_t new_table_iterator_nanos;
  // Time spent on seeking a key in data/index blocks
  uint64_t block_seek_nanos;
  // Time spent on finding or creating a table reader
  uint64_t find_table_nanos;
  // total number of mem table bloom hits
  uint64_t bloom_memtable_hit_count;
  // total number of mem table bloom misses
  uint64_t bloom_memtable_miss_count;
  // total number of SST table bloom hits
  uint64_t bloom_sst_hit_count;
  // total number of SST table bloom misses
  uint64_t bloom_sst_miss_count;

  // Time spent waiting on key locks in transaction lock manager.
  uint64_t key_lock_wait_time;
  // number of times acquiring a lock was blocked by another transaction.
  uint64_t key_lock_wait_count;

  // Total time spent in Env filesystem operations. These are only populated
  // when TimedEnv is used.
  uint64_t env_new_sequential_file_nanos;
  uint64_t env_new_random_access_file_nanos;
  uint64_t env_new_writable_file_nanos;
  uint64_t env_reuse_writable_file_nanos;
  uint64_t env_new_random_rw_file_nanos;
  uint64_t env_new_directory_nanos;
  uint64_t env_file_exists_nanos;
  uint64_t env_get_children_nanos;
  uint64_t env_get_children_file_attributes_nanos;
  uint64_t env_delete_file_nanos;
  uint64_t env_create_dir_nanos;
  uint64_t env_create_dir_if_missing_nanos;
  uint64_t env_delete_dir_nanos;
  uint64_t env_get_file_size_nanos;
  uint64_t env_get_file_modification_time_nanos;
  uint64_t env_rename_file_nanos;
  uint64_t env_link_file_nanos;
  uint64_t env_lock_file_nanos;
  uint64_t env_unlock_file_nanos;
  uint64_t env_new_logger_nanos;

  uint64_t get_cpu_nanos;
  uint64_t iter_next_cpu_nanos;
  uint64_t iter_prev_cpu_nanos;
  uint64_t iter_seek_cpu_nanos;

  // Time spent in encrypting data. Populated when EncryptedEnv is used.
  uint64_t encrypt_data_nanos;
  // Time spent in decrypting data. Populated when EncryptedEnv is used.
  uint64_t decrypt_data_nanos;

  std::map<uint32_t, PerfContextByLevel>* level_to_perf_context = nullptr;
  bool per_level_perf_context_enabled = false;
};

// If RocksDB is compiled with -DNPERF_CONTEXT, then a pointer to a global,
// non-thread-local PerfContext object will be returned. Attempts to update
// this object will be ignored, and reading from it will also be no-op.
// Otherwise,
// a) if thread-local is supported on the platform, then a pointer to
//    a thread-local PerfContext object will be returned.
// b) if thread-local is NOT supported, then compilation will fail.
//
// This function never returns nullptr.
PerfContext* get_perf_context();

}  // namespace ROCKSDB_NAMESPACE