Runtime Metrics

Runtime metrics are used to collect the metrics of important velox runtime events for monitoring purpose. The collected metrics can provide insights into the continuous availability and performance analysis of a Velox runtime system. For instance, the collected data can help automatically generate alerts at an outage. Velox provides a framework to collect the metrics which consists of three steps:

Define: define the name and type for the metric through DEFINE_METRIC and DEFINE_HISTOGRAM_METRIC macros. DEFINE_HISTOGRAM_METRIC is used for histogram metric type and DEFINE_METRIC is used for the other types (see metric type definition below). BaseStatsReporter provides methods for metric definition. Register metrics during startup using registerVeloxMetrics() API.

Record: record the metric data point using RECORD_METRIC_VALUE and RECORD_HISTOGRAM_METRIC_VALUE macros when the corresponding event happens. BaseStatsReporter provides methods for metric recording.

Export: aggregates the collected data points based on the defined metrics, and periodically exports to the backend monitoring service, such as ODS used by Meta, Apache projects OpenCensus and Prometheus provided by OSS. A derived implementation of BaseStatsReporter is required to integrate with a specific monitoring service. The metric aggregation granularity and export interval are also configured based on the actual used monitoring service.

Velox supports five metric types:

Count: tracks the count of events, such as the number of query failures.

Sum: tracks the sum of event data point values, such as sum of query scan read bytes.

Avg: tracks the average of event data point values, such as average of query execution time.

Rate: tracks the sum of event data point values per second, such as the number of shuffle requests per second.

Histogram: tracks the distribution of event data point values, such as query execution time distribution. The histogram metric divides the entire data range into a series of adjacent equal-sized intervals or buckets, and then count how many data values fall into each bucket. DEFINE_HISTOGRAM_METRIC specifies the data range by min/max values, and the number of buckets. Any collected data value less than min is counted in min bucket, and any one larger than max is counted in max bucket. It also allows to specify the value percentiles to report for monitoring. This allows BaseStatsReporter and the backend monitoring service to optimize the aggregated data storage.

Task Execution

Metric Name	Type	Description
driver_yield_count	Count	The number of times that a driver has yielded from the thread when it hits the per-driver cpu time slice limit if enforced.
driver_queue_time_ms	Histogram	The distribution of driver queue latency in range of [0, 10s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
driver_exec_time_ms	Histogram	The distribution of driver execution time in range of [0, 30s] with 30 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.

Memory Management

Metric Name	Type	Description
cache_shrink_count	Count	The number of times that in-memory data cache has been shrunk under memory pressure.
cache_shrink_ms	Histogram	The distribution of cache shrink latency in range of [0, 100s] with 10 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
memory_reclaim_count	Count	The count of operator memory reclaims.
memory_reclaim_exec_ms	Histogram	The distribution of memory reclaim execution time in range of [0, 600s] with 20 buckets. It is configured to report latency at P50, P90, P99, and P100 percentiles.
memory_reclaim_bytes	Histogram	The distribution of reclaimed bytes in range of [0, 4GB] with 64 buckets and reports P50, P90, P99, and P100.
task_memory_reclaim_count	Count	The count of task memory reclaims.
task_memory_reclaim_wait_ms	Histogram	The distribution of task memory reclaim wait time in range of [0, 60s] with 60 buckets. It is configured to report latency at P50, P90, P99, and P100 percentiles.
task_memory_reclaim_exec_ms	Histogram	The distribution of task memory execution time in range of [0, 240s] with 60 buckets. It is configured to report latency at P50, P90, P99, and P100 percentiles.
task_memory_reclaim_wait_timeout_count	Count	The number of times that the task memory reclaim wait timeouts.
memory_non_reclaimable_count	Count	The number of times that the memory reclaim fails because the operator is executing a non-reclaimable section where it is expected to have reserved enough memory to execute without asking for more. Therefore, it is an indicator that the memory reservation is not sufficient. It excludes counting instances where the operator is in a non-reclaimable state due to currently being on-thread and running or being already cancelled.
arbitrator_requests_count	Count	The number of times a memory arbitration request was initiated by a memory pool attempting to grow its capacity.
arbitrator_local_arbitration_count	Count	The number of arbitration that reclaims the used memory from the query which initiates the memory arbitration request itself. It ensures the memory arbitration request won’t exceed its per-query memory capacity limit.
arbitrator_global_arbitration_count	Count	The number of arbitration which ensures the total allocated query capacity won’t exceed the arbitrator capacity limit. It may or may not reclaim memory from the query which initiate the memory arbitration request. This indicates the velox runtime doesn’t have enough memory to run all the queries at their peak memory usage. We have to trigger spilling to let them run through completion.
arbitrator_slow_global_arbitration_count	Count	The number of global arbitration that reclaims used memory by slow disk spilling.
arbitrator_aborted_count	Count	The number of times a query level memory pool is aborted as a result of a memory arbitration process. The memory pool aborted will eventually result in a cancelling the original query.
arbitrator_failures_count	Count	The number of times a memory arbitration request failed. This may occur either because the requester was terminated during the processing of its request, the arbitration request would surpass the maximum allowed capacity for the requester, or the arbitration process couldn’t release the requested amount of memory.
arbitrator_wait_time_ms	Histogram	The distribution of the amount of time an arbitration request stays in arbitration queues and waits the arbitration r/w locks in range of [0, 600s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
arbitrator_arbitration_time_ms	Histogram	The distribution of the amount of time it take to complete a single arbitration request stays queued in range of [0, 600s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
arbitrator_free_capacity_bytes	Average	The average of total free memory capacity which is managed by the memory arbitrator.
arbitrator_free_reserved_capacity_bytes	Average	The average of free memory capacity reserved to ensure each query has the minimal required capacity to run.
memory_pool_initial_capacity_bytes	Histogram	The distribution of a root memory pool’s initial capacity in range of [0 256MB] with 32 buckets. It is configured to report the capacity at P50, P90, P99, and P100 percentiles.
memory_pool_capacity_growth_count	Histogram	The distribution of a root memory pool cappacity growth attemps through memory arbitration in range of [0, 256] with 32 buckets. It is configured to report the count at P50, P90, P99, and P100 percentiles.
memory_pool_usage_leak_bytes	Sum	The leaf memory pool usage leak in bytes.
memory_pool_reservation_leak_bytes	Sum	The leaf memory pool reservation leak in bytes.
memory_pool_capacity_leak_bytes	Sum	The root memory pool reservation leak in bytes.
memory_allocator_double_free_count	Count	Tracks the count of double frees in memory allocator, indicating the possibility of buffer ownership issues when a buffer is freed more than once.
memory_allocator_mapped_bytes	Avg	Number of bytes currently mapped in MemoryAllocator. These bytes represent the bytes that are either currently being allocated or were in the past allocated, not yet been returned back to the operating system, in the form of ‘Allocation’ or ‘ContiguousAllocation’.
memory_allocator_alloc_bytes	Avg	Number of bytes currently allocated (used) from MemoryAllocator in the form of ‘Allocation’ or ‘ContiguousAllocation’.
mmap_allocator_external_mapped_bytes	Avg	Number of bytes currently mapped in MmapAllocator, in the form of ‘ContiguousAllocation’. NOTE: This applies only to MmapAllocator
mmap_allocator_delegated_alloc_bytes	Avg	Number of bytes currently allocated from MmapAllocator directly from raw allocateBytes() interface, and internally allocated by malloc. Only small chunks of memory are delegated to malloc NOTE: This applies only to MmapAllocator

Cache

Metric Name	Type	Description
cache_max_age_secs	Avg	Max possible age of AsyncDataCache and SsdCache entries since the raw file was opened to load the cache.
memory_cache_num_entries	Avg	Total number of cache entries.
memory_cache_num_empty_entries	Avg	Total number of cache entries that do not cache anything.
memory_cache_num_shared_entries	Avg	Total number of cache entries that are pinned for shared access.
memory_cache_num_exclusive_entries	Avg	Total number of cache entries that are pinned for exclusive access.
memory_cache_num_prefetched_entries	Avg	Total number of cache entries that are being or have been prefetched but have not been hit.
memory_cache_total_tiny_bytes	Avg	Total number of bytes of the cached data that is much smaller than kTinyDataSize.
memory_cache_total_large_bytes	Avg	Total number of bytes of the cached data excluding ‘memory_cache_total_tiny_bytes’
memory_cache_total_tiny_padding_bytes	Avg	Total unused capacity bytes in ‘memory_cache_total_tiny_bytes’.
memory_cache_total_large_padding_bytes	Avg	Total unused capacity bytes in ‘memory_cache_total_large_bytes’.
memory_cache_total_prefetched_bytes	Avg	Total bytes of cache entries in prefetch state.
memory_cache_sum_evict_score	Sum	Sum of scores of evicted entries. This serves to infer an average lifetime for entries in cache.
memory_cache_num_hits	Sum	Number of hits (saved IO) since last counter retrieval. The first hit to a prefetched entry does not count.
memory_cache_hit_bytes	Sum	Amount of hit bytes (saved IO) since last counter retrieval. The first hit to a prefetched entry does not count.
memory_cache_num_new	Sum	Number of new entries created since last counter retrieval.
memory_cache_num_evicts	Sum	Number of times a valid entry was removed in order to make space, since last counter retrieval.
memory_cache_num_savable_evicts	Sum	Number of times a valid entry was removed in order to make space but has not been saved to SSD yet, since last counter retrieval.
memory_cache_num_evict_checks	Sum	Number of entries considered for evicting, since last counter retrieval.
memory_cache_num_wait_exclusive	Sum	Number of times a user waited for an entry to transit from exclusive to shared mode, since last counter retrieval.
memory_cache_num_alloc_clocks	Sum	Clocks spent in allocating or freeing memory for backing cache entries, since last counter retrieval
memory_cache_num_aged_out_entries	Sum	Number of AsyncDataCache entries that are aged out and evicted. given configured TTL.
memory_cache_num_stale_entries	Count	Number of AsyncDataCache entries that are stale because of cache request size mismatch.
ssd_cache_cached_regions	Avg	Number of regions currently cached by SSD.
ssd_cache_cached_entries	Avg	Number of entries currently cached by SSD.
ssd_cache_cached_bytes	Avg	Total bytes currently cached by SSD.
ssd_cache_read_entries	Sum	Total number of entries read from SSD.
ssd_cache_read_bytes	Sum	Total number of bytes read from SSD.
ssd_cache_written_entries	Sum	Total number of entries written to SSD.
ssd_cache_written_bytes	Sum	Total number of bytes written to SSD.
ssd_cache_aged_out_entries	Sum	Total number of SsdCache entries that are aged out and evicted given configured TTL.
ssd_cache_aged_out_regions	Sum	Total number of SsdCache regions that are aged out and evicted given configured TTL.
ssd_cache_open_ssd_errors	Sum	Total number of SSD file open errors.
ssd_cache_open_checkpoint_errors	Sum	Total number of SSD checkpoint file open errors.
ssd_cache_open_log_errors	Sum	Total number of SSD evict log file open errors.
ssd_cache_delete_checkpoint_errors	Sum	Total number of errors while deleting SSD checkpoint files.
ssd_cache_read_without_checksum	Sum	Total number of SSD cache reads without checksum verification due to SSD cache request size mismatch
ssd_cache_grow_file_errors	Sum	Total number of errors while growing SSD cache files.
ssd_cache_write_ssd_errors	Sum	Total number of error while writing to SSD cache files.
ssd_cache_write_ssd_dropped	Sum	Total number of writes dropped due to no cache space.
ssd_cache_write_checkpoint_errors	Sum	Total number of errors while writing SSD checkpoint file.
ssd_cache_read_corruptions	Sum	Total number of corrupted SSD data read detected by checksum.
ssd_cache_read_ssd_errors	Sum	Total number of errors while reading from SSD cache files.
ssd_cache_read_checkpoint_errors	Sum	Total number of errors while reading from SSD checkpoint files.
ssd_cache_checkpoints_read	Sum	Total number of checkpoints read.
ssd_cache_checkpoints_written	Sum	Total number of checkpoints written.
ssd_cache_regions_evicted	Sum	Total number of cache regions evicted.
ssd_cache_recovered_entries	Sum	Total number of cache entries recovered from checkpoint.

Storage

Metric Name	Type	Description
storage_throttled_duration_ms	Histogram	The time distribution of storage IO throttled duration in range of [0, 30s] with 30 buckets. It is configured to report the capacity at P50, P90, P99, and P100 percentiles.
storage_local_throttled_count	Count	The number of times that storage IOs get throttled in a storage directory.
storage_global_throttled_count	Count	The number of times that storage IOs get throttled in a storage cluster.

Spilling

Metric Name	Type	Description
spill_max_level_exceeded_count	Count	The number of times that a spill-able operator hits the max spill level limit.
spill_input_bytes	Sum	The number of bytes in memory to spill.
spill_bytes	Sum	The number of bytes spilled to disk which can be the number of compressed bytes if compression is enabled.
spill_rows_count	Count	The number of spilled rows.
spill_files_count	Count	The number of spilled files.
spill_fill_time_ms	Histogram	The distribution of the amount of time spent on filling rows for spilling in range of [0, 600s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
spill_sort_time_ms	Histogram	The distribution of the amount of time spent on sorting rows for spilling in range of [0, 600s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
spill_serialization_time_ms	Histogram	The distribution of the amount of time spent on serializing rows for spilling in range of [0, 600s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
spill_disk_writes_count	Count	The number of disk writes to spill rows.
spill_flush_time_ms	Histogram	The distribution of the amount of time spent on copy out serialized rows for disk write in range of [0, 600s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles. Note: If compression is enabled, this includes the compression time.
spill_write_time_ms	Histogram	The distribution of the amount of time spent on writing spilled rows to disk in range of [0, 600s] with 20 buckets. It is configured to report the latency at P50, P90, P99, and P100 percentiles.
file_writer_early_flushed_raw_bytes	Sum	Number of bytes pre-maturely flushed from file writers because of memory reclaiming.
spill_memory_bytes	Avg	The current spilling memory usage in bytes.
spill_peak_memory_bytes	Avg	The peak spilling memory usage in bytes.

Exchange

Metric Name	Type	Description
exchange_data_time_ms	Histogram	The distribution of data exchange latency in range of [0, 50s] with 50 buckets. It is configured to report latency at P50, P90, P99, and P100 percentiles.
exchange_data_bytes	Sum	The exchange data size in bytes.
exchange_data_size	Histogram	The distribution of exchange data size in range of [0, 128MB] with 128 buckets. It is configured to report the capacity at P50, P90, P99, and P100 percentiles.
exchange_data_count	Count	The number of data exchange requests.
exchange_data_size_time_ms	Histogram	The distribution of data exchange size latency in range of [0, 5s] with 50 buckets. It is configured to report latency at P50, P90, P99, and P100 percentiles.
exchange_data_size_count	Count	The number of data size exchange requests.

Hive Connector

Metric Name	Type	Description
hive_file_handle_generate_latency_ms	Histogram	The distribution of hive file open latency in range of [0, 100s] with 10 buckets. It is configured to report latency at P50, P90, P99, and P100 percentiles.