> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# Metrics Reference for mongot

The `mongot` process exposes Prometheus metrics that describe its runtime health and performance across core areas of operation. This reference page describes key metrics that are relevant to day-to-day monitoring and troubleshooting. For the complete metric set, scrape the `mongot` Prometheus metrics endpoint at `http://<mongot-host>:9946/metrics`.

## View Metrics

To view the raw metrics that `mongot` exposes, send an HTTP `GET` request to the following `mongot` Prometheus metrics endpoint:

```text
http://<mongot-host>:9946/metrics
```

In this endpoint:

- `<mongot-host>` is the hostname or IP address of the `mongot` process.

- `9946` is the default port for the metrics endpoint. To configure the metrics endpoint port, see the `metrics.address` setting in the `mongot` configuration file.

- `/metrics` is the path for the metrics endpoint.

The `/metrics` endpoint returns metrics in plain Prometheus text format. To monitor `mongot` metrics over time, configure your Prometheus instance to scrape this endpoint.

**Important:**

The `/metrics` endpoint requires no authentication by default. For production deployments, restrict access at the network layer.

## Metric Naming Conventions

`mongot` metric names use a consistent naming pattern:

- All metric names start with the `mongot_` prefix.

- Metric names generally follow the pattern `mongot_<area>_<measurement>[_<unit>]`, where:

  - `<area>` indicates the subsystem or component the metric belongs to, such as `process`, `jvm`, `replication`, or `index`.

  - `<measurement>` indicates what is being measured, such as `cpu_usage`, `heap_memory`, or `index_size`.

  - `<unit>` (optional) indicates the unit or counter semantics for the metric. This optional suffix indicates either the unit that the metric is measured in, such as `seconds`, `bytes`, or `ms`, or the type of counter the metric represents, such as `total`, `events`, or `operations`.

    **Note:**

    Some metric name suffixes don't reflect the actual reported unit for the metric. For example, `mongot_index_stats_query_latency_seconds` has the suffix `_seconds`, but `mongot` reports the metric in milliseconds, as indicated by the `timeUnit=milliseconds` label in the metric output. To confirm the unit for each metric, check the Unit value in the metric reference tables below.

In addition to the metric name, `mongot` metrics can include labels (also called dimensions). Labels distinguish multiple time series that share the same base metric name. For example, a metric might use labels to identify a `state`, `status`, `index type`, `quantile`, or a specific `index`.

For some metrics, you must interpret the metric as the combination of the metric name and its labels, not by the metric name alone. For example, `mongot_replication_mongodb_indexManagerState` uses the `state` label to expose one series for each replication state, such as `STEADY_STATE` or `FAILED`. Exactly one of those labeled series has the value `1` at a time. Per-index metrics similarly use labels such as `generationId_logString` and `indexId_logString` to distinguish one index from another.

For distribution metrics, the suffix of the metric name indicates the Prometheus series type:

- Histograms expose `_bucket`, `_count`, `_sum`, and `_max`.

- Summaries expose `_count`, `_sum`, and `_max`. Some summaries also include quantile labels such as `{quantile="0.5"}`.

### Common Metric Labels

The following table describes common labels that appear in `mongot` metrics.

| Label Name | Metric Scope | Possible Values |
| --- | --- | --- |
| `name` | All executor pools | `executorMetrics` |
| `Scope` | Cross-cutting | `jvm`, `replication`, `lucene` |
| `generationId_logString`, `indexId_logString` | Most `mongot_index_stats_*` series | Internal opaque Ids (the per-index identifier that the logs use) |
| `indexFeatureVersion` | Many index metrics | `3`, `5`, `6` (the on-disk index format) |
| `indexType` | Indexing and initial-sync metrics | `search`, `vector_search`, `vector_search_auto_embedding` (only when you configure Automated Embedding) |
| `numPartitions` | Index size and document metrics | `1` for self-managed |
| `timeUnit` | Latency summary metrics | `seconds`, `milliseconds`, `microseconds` |
| `quantile` | Summary metrics | `0.5`, `0.75`, `0.9`, `0.99` |
| `state` | `indexManagerState` | `STEADY_STATE`, `INITIAL_SYNC`, `INITIAL_SYNC_BACKOFF`, `INITIALIZING`, `FAILED`, `FAILED_EXCEEDED`, `SHUT_DOWN`, `STEADY_STATE_SHUT_DOWN` |
| `status` | `indexStatusCode` | `STEADY`, `INITIAL_SYNC`, `FAILED`, `RECOVERING_NON_TRANSIENT`, `RECOVERING_TRANSIENT`, `STALE`, `NOT_STARTED`, `DOES_NOT_EXIST`, `UNKNOWN` |
| `clientName` | `mongot_mongoClient_connectionPool_*` | `mongot steady state sync`, `mongot initial sync and session
                refresh`, `mongot metadata service`, `mongot periodic optime
                fetcher`, `mongot database metadata resolver`, `mongot server
                info resolver`, `mongot Lease Manager mongo client`, `mongot
                AutoEmbedding Materialized View Writer` (only when Automated Embedding is enabled) |

## Key Metric Groups

### Process and JVM Metrics

Use process and JVM (Java Virtual Machine) metrics to confirm that `mongot` is running normally and to identify heap or garbage collection pressure.

#### Process

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_process_uptime_seconds` | gauge | seconds | The uptime of the Java Virtual Machine. |
| `mongot_process_start_time_seconds` | gauge | unix seconds | Start time of the process since unix epoch. |
| `mongot_process_cpu_time_ns_total` | counter | nanoseconds | The "cpu time" used by the Java Virtual Machine process. Use `rate()` for instantaneous CPU consumption. |
| `mongot_process_cpu_usage` | gauge | 0-1 | The "recent cpu usage" for the Java Virtual Machine process. The value is normalized to a range of 0 to 1, where 1 represents full CPU utilization. |

#### JVM Memory

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_jvm_memory_used_bytes` | gauge | bytes | The amount of used memory. Labels: `area=heap|nonheap`, `id=<pool>` (for example, G1 Eden Space, G1 Old Gen, G1 Survivor Space, Metaspace). |
| `mongot_jvm_memory_committed_bytes` | gauge | bytes | The amount of memory committed for the Java virtual machine to use. |
| `mongot_jvm_memory_max_bytes` | gauge | bytes | The maximum memory that can be used. For heap, `id="G1 Old Gen"` carries `-Xmx`. |
| `mongot_jvm_buffer_count_buffers` | gauge | count | NIO buffer pool counts. Labels: `id=direct|mapped`. |
| `mongot_jvm_buffer_memory_used_bytes` | gauge | bytes | Memory the JVM uses for NIO buffer pools. |
| `mongot_jvm_buffer_total_capacity_bytes` | gauge | bytes | NIO buffer pool capacity. |

#### JVM Garbage Collection

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_jvm_gc_pause_seconds` | summary | seconds | Time spent in GC pause. No quantile labels. Use `mongot_jvm_gc_pause_seconds_max` for the longest recent pause. |
| `mongot_jvm_gc_concurrent_phase_time_seconds` | summary | seconds | Time spent in concurrent GC phase. |
| `mongot_jvm_gc_live_data_size_bytes` | gauge | bytes | Size of long-lived heap memory pool after reclamation. The "live heap" to watch for memory pressure. |
| `mongot_jvm_gc_max_data_size_bytes` | gauge | bytes | Max size of long-lived heap memory pool. |
| `mongot_jvm_gc_memory_allocated_bytes_total` | counter | bytes | Increase in young heap pool size between GCs. |
| `mongot_jvm_gc_memory_promoted_bytes_total` | counter | bytes | Promotions from young into old generation. |

### System Metrics

Use system metrics to monitor host-level CPU, disk, memory, paging, and network conditions that can affect `mongot`.

#### CPU

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_system_cpu_count` | gauge | count | Processors available to the JVM. |
| `mongot_system_cpu_usage` | gauge | 0-1 | Recent system CPU usage. The value is normalized to a range of 0 to 1, where 1 represents full CPU utilization. |
| `mongot_system_load_average_1m` | gauge | unitless | OS 1-minute load average. |

#### Disk

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_system_disk_space_data_path_free_bytes` | gauge | bytes | Free disk space on the `mongot` `dataPath` volume. Alert on this metric. |
| `mongot_system_disk_space_data_path_total_bytes` | gauge | bytes | Total disk space on the `dataPath` volume. Use to compute free %. |
| `mongot_system_disk_space_free_bytes`, `mongot_system_disk_space_total_bytes` | gauge | bytes | Free and total disk space across the file system (different scope than `data_path`). |
| `mongot_system_disk_readBytes_bytes` | gauge | bytes | Bytes read from disk per device. Label: `name=<device>` (e.g., `/dev/vda`). |
| `mongot_system_disk_writeBytes_bytes` | gauge | bytes | Bytes written per device. |
| `mongot_system_disk_reads_events` | gauge | count | Read I/O count per device. Use `rate()` for read IOPS. |
| `mongot_system_disk_writes_events` | gauge | count | Write I/O count per device. |
| `mongot_system_disk_currentQueueLength_tasks` | gauge | count | Disk queue length (I/Os in progress) per device. |
| `mongot_system_disk_transferTime_ms` | gauge | milliseconds | Time spent reading or writing per device. |

#### Memory

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_system_memory_phys_total_bytes` | gauge | bytes | Total physical memory on the host. |
| `mongot_system_memory_phys_available_bytes` | gauge | bytes | Physical memory available. |
| `mongot_system_memory_phys_inUse_bytes` | gauge | bytes | Physical memory in use. |
| `mongot_system_memory_virt_inUse_bytes` | gauge | bytes | Total physical and virtual memory in use. |
| `mongot_system_memory_virt_swap_inUse_bytes`, `mongot_system_memory_virt_swap_available_bytes`, `mongot_system_memory_virt_swap_total_bytes` | gauge | bytes | Swap state. |
| `mongot_system_memory_virt_swap_pagesIn_operations`, `mongot_system_memory_virt_swap_pagesOut_operations` | gauge | count | Swap in/out activity. |
| `mongot_system_memory_memoryMappings_objects` | gauge | count | Number of memory mappings (relevant for Lucene mmap counts). |
| `mongot_system_memory_pageSize_bytes` | gauge | bytes | System page size. |

#### Page Faults

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_system_process_majorPageFaults_operations` | gauge | count | Major page faults. Use this metric with the storage class advisory threshold. |
| `mongot_system_process_minorPageFaults_operations` | gauge | count | Minor page faults. |

#### Network

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_system_netstat_bytesRecv_bytes`, `mongot_system_netstat_bytesSent_bytes` | gauge | bytes | Bytes received and sent per interface (`name=eth0`). |
| `mongot_system_netstat_packetsRecv_events`, `mongot_system_netstat_packetsSent_events` | gauge | count | Packets received and sent. |
| `mongot_system_netstat_inErrors_events`, `mongot_system_netstat_outErrors_events`, `mongot_system_netstat_inDrops_events`, `mongot_system_netstat_collisions_events` | gauge | count | Error, drop, and collision counters. |
| `mongot_system_netstat_speed` | gauge | bits/sec | Negotiated interface speed. |

### Replication Metrics

Use replication metrics to determine whether `mongot` is healthy, syncing normally, and staying caught up with `mongod`.

#### Overall State

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_replication_manager` | gauge | 0/1 | `1` when the replication manager is active. |
| `mongot_replication_mongodb_manager` | gauge | 0/1 | `1` when the MongoDB-backed replication manager is active. Label: `type=normal`. |
| `mongot_replicationIndexManager_transitionState_total` | counter | count | State transitions. Labels: `fromState`, `toState`. Use to detect resyncs (`INITIALIZING` to `STEADY_STATE` transitions). |

#### Session Refresher

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_replication_sessionRefresher_sessions` | gauge | count | Active sessions. |
| `mongot_replication_sessionRefresher_refreshes_total` | counter | count | Total session refreshes. |
| `mongot_replication_sessionRefresher_failedSessionRefreshes_total` | counter | count | Failed refreshes. |
| `mongot_replication_sessionRefresher_sessionRefreshDurations_seconds` | summary | seconds | Refresh duration distribution. |

#### Optime Updater

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_replicationOptimeUpdaterError_total` | counter | count | Optime-update errors. |
| `mongot_replicationOptimeUpdater_executor_*` | various | N/A | Executor metrics for the optime updater. |

### Per-index Metrics

`mongot` emits the following metrics per index and includes `generationId_logString` and `indexId_logString` labels to identify the specific index. Filter by those labels to inspect a specific index, or aggregate across labels to understand fleet-wide behavior.

#### Index Status and Size

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_index_stats_indexStatusCode` | gauge | 0/1 | Per-index status. One-hot encoded across the `status` label values: `STEADY`, `INITIAL_SYNC`, `FAILED`, `RECOVERING_NON_TRANSIENT`, `RECOVERING_TRANSIENT`, `STALE`, `NOT_STARTED`, `DOES_NOT_EXIST`, `UNKNOWN`. |
| `mongot_index_stats_indexFeatureVersion` | gauge | number | On-disk index format version. For example, `3`. |
| `mongot_index_stats_indexSizeBytes` | gauge | bytes | Total on-disk size of the index. |
| `mongot_index_stats_largestIndexFileSizeBytes` | gauge | bytes | Largest single file in the index. |
| `mongot_index_stats_numFilesInIndex` | gauge | count | Number of Lucene segment files. |
| `mongot_index_stats_numLuceneDocs` | gauge | count | Lucene documents in the index. |
| `mongot_index_stats_numLuceneMaxDocs` | gauge | count | Maximum Lucene document ID (includes deleted-not-merged). |
| `mongot_index_stats_numLuceneFields` | gauge | count | Number of indexed Lucene fields. |
| `mongot_index_stats_segment_count` | gauge | count | Number of Lucene segments. |
| `mongot_index_stats_requiredMemoryBytes` | gauge | bytes | Estimated required memory for the index. |

#### Indexing Metrics

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_index_stats_indexing_replicationLagMs` | gauge | milliseconds | Replication lag per index, in milliseconds. The unit is in the metric name (`Ms`). Do not divide by 1000 in PromQL unless you want to convert to seconds. |
| `mongot_index_stats_indexing_replicationOpTime` | gauge | BSON Timestamp | Last applied replication optime (numeric encoding). |
| `mongot_index_stats_indexing_maxPossibleReplicationOpTime` | gauge | BSON Timestamp | Cap on advance, set by `mongod` tip. |
| `mongot_index_stats_indexing_insert_total`, `mongot_index_stats_indexing_update_total`, `mongot_index_stats_indexing_delete_total` | counter | count | Indexing operation counts. Label: `indexType=search`. |
| `mongot_index_stats_indexing_totalBytesProcessed_total` | counter | bytes | Total bytes processed by indexing. |
| `mongot_index_stats_indexing_vectorFieldsIndexed_total` | counter | count | Vector fields indexed. |
| `mongot_index_stats_indexing_commitDurations_seconds` | summary | seconds (`timeUnit=milliseconds`) | Per-index commit durations. |
| `mongot_index_stats_indexing_indexingBatchDurations_seconds` | summary | seconds | Batch duration distribution. |
| `mongot_index_stats_indexing_largeChangeStreamEvents_total` | counter | count | Oversized change-stream events. Label: `threshold=10MiB|12MiB|14MiB|15MiB`. |
| `mongot_index_stats_indexing_invalidGeometryField_total` | counter | count | Documents rejected for invalid geometry. |
| `mongot_index_stats_indexing_sortableStringTruncated_total` | counter | count | Truncated sortable strings. |
| `mongot_index_stats_indexing_initialSyncExceptions_total` | counter | count | Exceptions during initial sync. |
| `mongot_index_stats_indexing_steadyStateExceptions_total` | counter | count | Steady-state exceptions. |
| `mongot_index_stats_indexing_consecutiveInitialSyncResyncExceptions` | gauge | count | Consecutive initial-sync resync exceptions for this index. |

#### Query Metrics

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_index_stats_query_totalQueries_total` | counter | count | Total queries issued against the index. |
| `mongot_index_stats_query_totalHitsCount_total` | counter | count | Total hits returned. |
| `mongot_index_stats_query_failedQueries_total` | counter | count | Queries that failed. |
| `mongot_index_stats_query_internallyFailedQueries_total`, `mongot_index_stats_query_invalidQueries_total`, `mongot_index_stats_query_npeQueries_total`, `mongot_index_stats_query_lenientFailures_total` | counter | count | Specific failure-class counters. |
| `mongot_index_stats_query_searchResultBatchLatencies_seconds` | summary | seconds (`timeUnit=milliseconds`) | Search batch latency. This is the headline query-latency metric. |
| `mongot_index_stats_query_luceneTopDocsSearchLatencies_seconds` | summary | seconds (`timeUnit=milliseconds`) | Latency inside Lucene's TopDocs search. Use this metric to distinguish Lucene-internal latency from total latency. |
| `mongot_index_stats_query_vectorResultLatencies_seconds` | summary | seconds (`timeUnit=milliseconds`) | Vector search result latency. |
| `mongot_index_stats_query_vectorSearchInitialTopDocsLatencyTimer_seconds`, `mongot_index_stats_query_vectorSearchGetMoreTopDocsLatencyTimer_seconds` | summary | seconds (`timeUnit=milliseconds`) | Vector search latency phases. |
| `mongot_index_stats_query_tokenFacetsStateRefreshLatency_seconds` | summary | seconds (`timeUnit=milliseconds`) | Facets state-refresh latency. |
| `mongot_index_stats_query_batchDataSize`, `mongot_index_stats_query_batchDocumentCount` | summary | bytes / count | Per-batch payload size and document count. |
| `mongot_index_stats_query_limitPerQuery` | histogram | count (`le=10|50|100|200|500|1000|+Inf`) | Distribution of `$search` and `$vectorSearch` limits. |
| `mongot_index_stats_query_numCandidatesPerQuery` | histogram | count | Vector candidates per query, bucketed by quantization. |
| `mongot_index_stats_query_getMoreCommandCalls_total`, `mongot_index_stats_query_getMoreCommandCallsPerQuery` | counter / summary | count | `getMore` call counts. |
| `mongot_index_stats_query_batchWithTies_total` | counter | count | Result batches with score ties. |
| `mongot_index_stats_query_benefitFromIndexSortCount_total` | counter | count | Queries that benefited from index sort optimization. |
| `mongot_index_stats_query_extractableLimitQueries_total`, `mongot_index_stats_query_extractableLimitSecondBatchQueries_total` | counter | count | Limit-extraction optimizations triggered. |
| `mongot_index_stats_query_phantomSearcherCleanupCount_total` | counter | count | Phantom-searcher cleanups. |
| `mongot_index_stats_query_orphanedDeletedDocsRatio` | summary | ratio | Deleted-document ratio in returned results. |
| `mongot_index_stats_query_noProgressBatches_total` | counter | count | Batches that made no forward progress. |
| `mongot_index_stats_query_vectorCommandCalls_total`, `mongot_index_stats_query_vectorRescoringFailureCount_total`, `mongot_index_stats_query_vectorSearchQueriesOverSearchIndexes_total` | counter | count | Vector-specific counters. |
| `mongot_index_stats_query_feature_total` | counter | count | Per-query-feature usage. Label: `name=<feature>`. For example, `compound`, `text`, `phrase`, `near`, `vectorSearch`, `knnBeta`, `autoEmbedding` (only when Automated Embedding is enabled). |
| `mongot_index_stats_query_failedExplainQueryAggregate_total` | counter | count | Failed `$explain` aggregates. |

#### Per-index Replication Breakdown

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_replication_mongodb_indexManagerState` | gauge | 0/1 | The canonical replication-state signal. `mongot` one-hot encodes this metric, meaning that exactly one `state` label is `1.0`. States: `STEADY_STATE`, `INITIAL_SYNC`, `INITIAL_SYNC_BACKOFF`, `INITIALIZING`, `FAILED`, `FAILED_EXCEEDED`, `SHUT_DOWN`, `STEADY_STATE_SHUT_DOWN`. |
| `mongot_index_stats_replication_steadyState_batchTotalApplicableBytes`, `mongot_index_stats_replication_steadyState_batchTotalApplicableDocuments` | summary | bytes / count | Steady-state batch sizes. |
| `mongot_index_stats_replication_steadyState_decodingBatchDurations_seconds` | summary | seconds | Steady-state decoding duration. |
| `mongot_index_stats_replication_steadyState_getMoreDurations_seconds` | summary | seconds | Steady-state `getMore` duration. |
| `mongot_index_stats_replication_initialSync_changeStream_*` | summary | — | Initial-sync change-stream phase metrics (mirrors steady state). |
| `mongot_index_stats_replication_initialSync_collScan_*` | summary | — | Initial-sync collection-scan phase metrics. |

#### Lucene Refresh Latency

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_index_stats_luceneIndexRefresher_refreshDurations_seconds` | summary | seconds (`timeUnit=milliseconds`) | Lucene IndexReader refresh latency. |

### Command Metrics

`mongot` accepts the following set of named commands from `mongod`:

- `buildinfo`

- `getMore`

- `hello`

- `isMaster`

- `ismaster`

- `killCursors`

- `manageSearchIndex`

- `ping`

- `planShardedSearch`

- `search`

- `vectorSearch`

For each command, `mongot` exposes the following metrics, where `<name>` is a placeholder for the command name:

| Pattern | Type | Description |
| --- | --- | --- |
| `mongot_command_<name>CommandFailure_total` | counter | Failure count for the command. |
| `mongot_command_<name>CommandTotalLatency_seconds` | summary | End-to-end latency including serialization. |
| `mongot_command_<name>CommandSerializationLatency_seconds` | summary | Serialization latency (subset; not all commands). |

**Tip: Monitor Search and Vector Search Latency Across Indexes**

`mongot_command_searchCommandTotalLatency_seconds` and `mongot_command_vectorSearchCommandTotalLatency_seconds` are the primary metrics to monitor for [`$search`](https://www.mongodb.com/docs/search/query/aggregation-stages/search.md#mongodb-pipeline-pipe.-search) and [`$vectorSearch`](https://www.mongodb.com/docs/vector-search/query/aggregation-stages/vector-search-stage.md#mongodb-pipeline-pipe.-vectorSearch) latency aggregates. These expose latency aggregates for all `search` and `vectorSearch` commands across all indexes.

### Indexing Scheduler and Dispatcher Metrics

Use indexing scheduler and dispatcher metrics to identify backlog, saturation, and slow work in replication and indexing pipelines.

#### Steady-state Change-stream Pipeline

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_indexing_steadyStateChangeStream_batchesInProgressTotal` | gauge | count | Batches currently being applied. Label: `indexType=search|vector_search| vector_search_auto_embedding` (only when you enable Automated Embedding). |
| `mongot_indexing_steadyStateChangeStream_batchesInProgressTotalDurations_seconds` | summary | seconds | Duration distribution for in-flight batches. |
| `mongot_indexing_steadyStateChangeStream_getMoreDurations_seconds` | summary | seconds | `getMore` round-trip distribution. |
| `mongot_indexing_steadyStateChangeStream_getMoresInFlight` | gauge | count | `getMore` requests in flight. |
| `mongot_indexing_steadyStateChangeStream_getMoresScheduled` | gauge | count | Scheduled `getMore` requests by `indexType`. |
| `mongot_indexing_steadyStateChangeStream_getMoresSchedulingDurations_seconds` | summary | seconds | `getMore` scheduling latency. |
| `mongot_indexing_steadyStateChangeStream_preprocessingBatchDurations_seconds` | summary | seconds | Pre-processing duration per batch. |
| `mongot_indexing_steadyStateChangeStream_witnessedChangeStreamUpdates_total` | counter | count | Total change-stream events observed. Label: `Scope=replication`. |
| `mongot_indexing_steadyStateChangeStream_applicableChangeStreamUpdates_total` | counter | count | Events that `mongot` considered applicable. |
| `mongot_indexing_steadyStateChangeStream_dispatcher` | gauge | 0/1 | Dispatcher status. Labels: `Scope=replication`, `client=synchronous-batch`. |
| `mongot_indexing_steadyStateChangeStream_skippedChangeStreamDocumentsWithoutMetadataNamespace_total` | counter | count | Events skipped due to missing metadata. |
| `mongot_indexing_steadyStateChangeStream_unexpectedBatchFailures_total` | counter | count | Unexpected batch failures. |
| `mongot_indexing_steadyStateChangeStream_rescheduledEmbeddingGetMores_total` | counter | count | Rescheduled embedding getMores. This metric is only available when you configure Automated Embedding. |
| `mongot_indexing_changeStreamModeSelector_failedSamplingAttemptsCounter_total` | counter | count | Failed change-stream mode sampling attempts. |

#### Indexing Work Scheduler

Indexing work scheduler metrics monitor the queueing and execution of indexing batches.

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_indexingWorkScheduler_queuedBatchesTotal`, `mongot_indexingWorkScheduler_queuedEventsTotal` | gauge | count | Scheduler queue depth. |
| `mongot_indexingWorkScheduler_enqueueCalls_total`, `mongot_indexingWorkScheduler_dequeueCalls_total` | counter | count | Enqueue and dequeue counts. |
| `mongot_indexingWorkScheduler_indexingBatchDistribution` | summary | count | Distribution of batch sizes. Label: `Scope=replication`. |
| `mongot_indexingWorkScheduler_indexingBatchDurations_seconds` | summary | seconds | Batch durations. |
| `mongot_indexingWorkScheduler_indexingBatchSchedulingDurations_seconds` | summary | seconds | Scheduling overhead. |

#### Decoding Work Scheduler

Decoding work scheduler metrics monitor the queueing and execution of change-stream batch decoding.

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_decodingWorkScheduler_queuedBatchesTotal`, `mongot_decodingWorkScheduler_queuedEventsTotal` | gauge | count | Scheduler queue depth. |
| `mongot_decodingWorkScheduler_enqueueCalls_total`, `mongot_decodingWorkScheduler_dequeueCalls_total` | counter | count | Enqueue and dequeue counts. |
| `mongot_decodingWorkScheduler_decodingBatchDistribution` | summary | count | Distribution of batch sizes. Label: `Scope=replication`. |
| `mongot_decodingWorkScheduler_decodingBatchDurations_seconds` | summary | seconds | Batch durations. |
| `mongot_decodingWorkScheduler_decodingBatchSchedulingDurations_seconds` | summary | seconds | Scheduling overhead. |

### Initial Sync, Lifecycle, and Config Metrics

Use these metrics to track index startup work, recovery, and catalog state.

#### Initial Sync

**Note:**

Some `mongot` metrics are phase-specific and populate only when the corresponding code path is active. For example, steady-state replication metrics, such as `mongot_index_stats_indexing_replicationLagMs` and the `mongot_index_stats_replication_steadyState_*` series, do not populate while an index is in initial sync. Conversely, initial-sync-specific metrics, such as `mongot_initialsync_*` and `mongot_index_stats_replication_initialSync_*`, are only relevant while initial sync is running or has run.

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_initialsync_queue_queuedSyncs` | gauge | count | Queued initial syncs. Label: `indexType`. |
| `mongot_initialsync_queue_requeuedEmbeddingInitialSyncs_total` | counter | count | Embedding initial syncs that were requeued.  This metric is only available when you configure Automated Embedding. |
| `mongot_initialsync_dispatcher_inProgressSyncs` | gauge | count | Initial syncs currently in progress. Label: `indexType`. |
| `mongot_initialsync_dispatcher_queuedSyncs` | gauge | count | Initial syncs queued at the dispatcher. |
| `mongot_initialsync_dispatcher_inProgressResumedSyncs` | gauge | count | In-progress syncs that resumed from a checkpoint. |
| `mongot_initialsync_dispatcher_collectionScan` | gauge | 0/1 | Active collection-scan mode. Label: `scan_type=id_order|natural_order`. |
| `mongot_initialsync_dispatcher_completedSyncDuration_seconds` | summary | seconds | Completed sync duration distribution. |
| `mongot_initialsync_dispatcher_syncDuration_seconds` | summary | seconds | Ongoing sync duration. |
| `mongot_initialsync_dispatcher_inProgressInitialSyncDurationMin_seconds`, `mongot_initialsync_dispatcher_inProgressInitialSyncDurationMax_seconds`, `mongot_initialsync_dispatcher_inProgressInitialSyncDurationSum_seconds` | gauge | seconds | Min, max, and sum of in-progress initial sync durations. |
| `mongot_initialsync_dispatcher_unreadableDroppedIndexes_total` | counter | count | Dropped because their on-disk segments could not be read. |
| `mongot_initialsync_dispatcher_unreadableIndexRecoveries_total` | counter | count | Recovered after unreadable segments. Label: `unreadableIndexCause=corruptIndex|incompatibleCodec|
                incompatibleIndexFormat`. |

#### Lifecycle

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_lifecycle_indexesInInitializedState` | gauge | count | Indexes currently in the initialized state. |
| `mongot_lifecycle_indexInitializationDuration_seconds` | summary | seconds | Initialization durations. |
| `mongot_lifecycle_failedDownloadIndexes_total` | counter | count | Index downloads that failed. |
| `mongot_lifecycle_failedDropIndexes_total` | counter | count | Index drops that failed. |
| `mongot_lifecycle_failedInitializationIndexes_total` | counter | count | Index initializations that failed. |

#### Config State

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_configState_indexesInCatalog` | gauge | count | Indexes currently in the catalog. Labels: `Scope=replication`, `indexFormatVersion`. |
| `mongot_configState_indexesPhasingOut` | gauge | count | Indexes being phased out. |
| `mongot_configState_stagedIndexes` | gauge | count | Staged but not yet active indexes. |
| `mongot_configState_indexesInCatalogFeatureVersionFour`, `mongot_configState_indexesPhasingOutFeatureVersionFour`, `mongot_configState_stagedIndexesFeatureVersionFour` | gauge | count | Feature-version-4-specific equivalents. |

### Cursors and Index Factory

Use these metrics to monitor open cursor state and to detect indexes that `mongot` dropped or recovered because their on-disk segments were unreadable.

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_cursorManager_trackedCursors` | gauge | count | Currently tracked open cursors. |
| `mongot_indexFactory_unreadableDroppedIndexes_total` | counter | count | Indexes dropped because their segments were unreadable. |
| `mongot_indexFactory_unreadableIndexRecoveries_total` | counter | count | Recoveries after unreadable segments. Label: `unreadableIndexCause`. |

### Lucene Merge

Use these metrics to monitor Lucene segment merge activity, including the number and size of merges in progress, merge input and output sizes, merge durations, and merges discarded by the disk-utilization merge policy.

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_mergeScheduler_currentlyRunningMerges` | gauge | count | Active merges. Label: `Scope=lucene`. |
| `mongot_mergeScheduler_currentlyMergingDocs` | gauge | count | Documents currently being merged. |
| `mongot_mergeScheduler_numMerges_total` | counter | count | Total merges executed since startup. |
| `mongot_mergeScheduler_numSegmentsMerged_total` | counter | count | Segments folded by merges. |
| `mongot_mergeScheduler_mergeSize` | summary | bytes | Distribution of merge input sizes. |
| `mongot_mergeScheduler_mergeResultSize` | summary | bytes | Distribution of merge output sizes. |
| `mongot_mergeScheduler_mergedDocs` | summary | count | Documents-per-merge distribution. |
| `mongot_mergeScheduler_mergeTime_seconds` | summary | seconds | Merge duration distribution. |
| `mongot_diskUtilizationAwarenessMergePolicy_discardedMerge_total` | counter | count | Merges discarded by the disk-utilization-aware policy. |

### MongoDB Client Connection Pool Metrics

`mongot` opens multiple named connection pools to `mongod`, and labels each pool with a `clientName` label that identifies the role of each pool. The following table lists possible `clientName` label values and their corresponding role:

| clientName | Purpose |
| --- | --- |
| `mongot steady state sync` | Steady-state change-stream replication. |
| `mongot initial sync and session refresh` | Initial sync and session refresh. The `appName` seen in `mongod` `currentOp`. |
| `mongot metadata service` | Internal metadata service. |
| `mongot periodic optime fetcher` | Optime polling. |
| `mongot database metadata resolver` | Database metadata lookups. |
| `mongot server info resolver` | Server-info lookups. |
| `mongot Lease Manager mongo client` | Lease manager. |
| `mongot AutoEmbedding Materialized View Writer` | Automated embedding writes. This connection pool only appears when you configure Automated Embedding. |

The following table lists the available metrics for `mongot` connection pools:

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_mongoClient_connectionPool_connections` | gauge | count | Currently open connections in the pool. |
| `mongot_mongoClient_connectionPool_connectionsCheckedOut` | gauge | count | Connections currently checked out. |
| `mongot_mongoClient_connectionPool_maxSize` | gauge | count | Configured max pool size. |
| `mongot_mongoClient_connectionPool_minSize` | gauge | count | Configured min pool size. |
| `mongot_mongoClientBuilder_successfulOpenSSLDynamicLinking_total` | counter | count | Successful native OpenSSL link attempts. |
| `mongot_mongoClientBuilder_failedOpenSSLDynamicLinking_total` | counter | count | Failed native OpenSSL link attempts. |

### Synonyms

Use these metrics to monitor synonym synchronization activity, including collection scans, scan and sync durations, queue depth, and exceptions encountered during synonym sync.

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_synonymSync_collScans_total` | counter | count | Total collection scans performed for synonyms. |
| `mongot_synonymSync_collScansTriggeredByChangeStream_total` | counter | count | Synonym scans triggered by change-stream events. |
| `mongot_synonymSync_collScanDurations_seconds` | summary | seconds | Scan duration distribution. |
| `mongot_synonymSync_syncDurations_seconds` | summary | seconds | Sync duration distribution. |
| `mongot_synonymSync_queueDepth` | gauge | count | Current synonym sync queue depth. |
| `mongot_synonymSync_exceptions_total` | counter | count | Synonym sync exceptions. |

### Executor Pools

Use these metrics to monitor the named executor pools that `mongot` uses to run background work. Each pool exposes the same set of sub-metrics, prefixed with the pool name, so you can track thread activity, pool sizing, queue depth, task throughput, and per-task execution time across all pools.

The following table lists the sub-metrics that every executor pool exposes, where `<pool>` is the pool name prefix. All executor-pool sub-metrics carry the label `name="executorMetrics"`.

| Sub-Metric Suffix | Type | Description |
| --- | --- | --- |
| `<pool>_active_threads` | gauge | Threads currently executing tasks. |
| `<pool>_pool_core_threads`, `<pool>_pool_max_threads`, `<pool>_pool_size_threads` | gauge | Pool sizing. |
| `<pool>_queued_tasks` | gauge | Tasks waiting for a thread — the saturation signal. |
| `<pool>_queue_remaining_tasks` | gauge | Remaining queue capacity. |
| `<pool>_completed_tasks_total` | counter | Tasks completed since startup. |
| `<pool>_idle_seconds` | summary | Time threads spent idle between tasks. |
| `<pool>_seconds` | summary | Per-task execution time. |
| `<pool>_scheduled_once_total`, `<pool>_scheduled_repetitively_total` | counter | Scheduled task counts (for scheduling pools). |

The following table lists the prefixes for all available named executor pools and their respective purposes:

| Executor Pool Prefix | What it runs |
| --- | --- |
| `mongot_blobstore_lifecycle_executor` | Blob-store lifecycle work. |
| `mongot_blocking_server_worker_executor` | Blocking gRPC server worker threads. |
| `mongot_change_stream_mode_selector_executor` | Change-stream mode selection. |
| `mongot_change_stream_sync_dispatcher_executor` | Change-stream sync dispatching (one of the busiest in steady state). |
| `mongot_config_monitor_executor` | Config-monitor polling. |
| `mongot_decoding_executor` | Decoding pipeline workers. |
| `mongot_disk_monitor_executor` | Disk-monitor polling. |
| `mongot_grpc_health_check_executor` | gRPC health check timer. |
| `mongot_idle_cursor_killer_executor` | Idle cursor reaping. |
| `mongot_index_commit_executor` | Index commit operations. |
| `mongot_index_lifecycle_executor` | Per-index lifecycle work. |
| `mongot_index_refresh_executor` | Lucene IndexReader refreshes. |
| `mongot_indexing_work_executor` | Indexing pipeline workers (the busiest indexing pool in steady state). |
| `mongot_indexing_lifecycle_executor` | Indexing-lifecycle work. |
| `mongot_indexing_auto_embedding_executor` | Automated-embedding indexing path.  This executor pool only appears when you configure Automated Embedding. |
| `mongot_init_lifecycle_executor` | Init-time lifecycle work. |
| `mongot_mat_view_commit_executor`, `mongot_mat_view_leader_heartbeat_executor`, `mongot_mat_view_optime_updater_executor`, `mongot_mat_view_status_refresh_executor`, `mongot_materialized_view_lifecycle_executor` | Materialized-view tracking and lifecycle. These metrics are only available when Automated Embedding or other materialized-view-backed features are configured. |
| `mongot_replicationOptimeUpdater_executor` | Optime updater (background). |
| `mongot_session_refresh_executor` | Session refresher. |
| `mongot_system_metrics_updater_executor` | System metrics updater. |

**Tip: Watch Saturation Across All Executor Pools**

To monitor saturation across all executor pools, run the following PromQL query:

```promql
max by (pool) (
  label_replace(
    {__name__=~"mongot_.+_executor_queued_tasks"},
    "pool", "$1", "__name__", "mongot_(.+)_executor_queued_tasks"
  )
)
```

This query returns the queued-task count for each executor pool.

### Prometheus Server Self-Metrics

The following metric is available for the embedded Prometheus server in `mongot`:

| Metric | Type | Unit | Description |
| --- | --- | --- | --- |
| `mongot_prometheus_server_scraping_timer_seconds` | summary | seconds (`timeUnit=milliseconds`) | How long `mongot` takes to assemble a `/metrics` response. Sustained growth here means metric exposition itself is slowing down. |

## Configuration-Specific Metrics

The following metric families appear in the `/metrics` output only when you enable specific features.

| Metric Family | Description | Availability in Self-Managed `mongot` |
| --- | --- | --- |
| `mongot_*embedding*` | Metrics related to Automated Embedding. For example, `mongot_initialsync_queue_requeuedEmbeddingInitialSyncs_total`, `mongot_materialized_view_lifecycle_executor`, and connection-pool entries with `clientName="mongot AutoEmbedding
                Materialized View Writer"`. | Appear only when you configure Automated Embedding. |
| `mongot_mongot_ftdc_executor_failure_total` | Failure count for the FTDC executor. | Appears only when you enable the `ftdcExecutorMetricsToPrometheus` feature flag. |

## PromQL Examples

Most latency metrics in this catalog are summaries, not histograms, so use their published `quantile` labels directly when they exist. A smaller number of metrics, such as `mongot_index_stats_query_limitPerQuery` and `mongot_index_stats_query_numCandidatesPerQuery`, are histograms and expose `_bucket` series.

```promql
# Replication state
max by (state) (mongot_replication_mongodb_indexManagerState)

# Number of search indexes at STEADY_STATE replication
mongot_replication_mongodb_indexManagerState{state="STEADY_STATE"}

# Maximum replication lag across all indexes, converted to seconds
max(mongot_index_stats_indexing_replicationLagMs) / 1000

# Index count by status
count by (status) (mongot_index_stats_indexStatusCode == 1)

# Search query p99 latency across all indexes
max(mongot_index_stats_query_searchResultBatchLatencies_seconds{quantile="0.99"})

# Worst recent GC pause
max(mongot_jvm_gc_pause_seconds_max)

# Average GC pause over 5 minutes
rate(mongot_jvm_gc_pause_seconds_sum[5m]) / rate(mongot_jvm_gc_pause_seconds_count[5m])

# Free disk percentage on dataPath
mongot_system_disk_space_data_path_free_bytes
  / mongot_system_disk_space_data_path_total_bytes

# Major page fault rate
rate(mongot_system_process_majorPageFaults_operations[5m])

# Steady-state and initial sync exceptions over 15 minutes
sum(rate(mongot_index_stats_indexing_steadyStateExceptions_total[15m]))
sum(rate(mongot_index_stats_indexing_initialSyncExceptions_total[15m]))
```