db.collection.stats()¶

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Definition
Behavior
Examples

Definition¶

db.collection.stats(<option>)¶

mongo Shell Method

This page documents the mongo shell method, and does not refer to the MongoDB Node.js driver (or any other driver) method. For corresponding MongoDB driver API, refer to your specific MongoDB driver documentation instead.

Returns statistics about the collection.

The method has the following format:

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db.collection.stats({
   scale: <num>,                   // Optional
   indexDetails: <boolean>,        // Optional
   indexDetailsKey: <document>,    // Optional
   indexDetailsName: <string>.     // Optional
})

Field	Type	Description
`scale`	number	Optional. The scale factor for the various size data. The `scale` defaults to 1 to return size data in bytes. To display kilobytes rather than bytes, specify a `scale` value of `1024`. If you specify a non-integer scale factor, MongoDB uses the integer part of the specified factor. For example, if you specify a scale factor of `1023.999`, MongoDB uses `1023` as the scale factor. Starting in version 4.2, the output includes the `scaleFactor` used to scale the size values.
`indexDetails`	boolean	Optional. If `true`, `db.collection.stats()` returns `index details` in addition to the collection stats. Only works for WiredTiger storage engine. Defaults to `false`.
`indexDetailsKey`	document	Optional. If `indexDetails` is `true`, you can use `indexDetailsKey` to filter index details by specifying the index key specification. Only the index that exactly matches `indexDetailsKey` will be returned. If no match is found, `indexDetails` will display statistics for all indexes. Use `getIndexes()` to discover index keys. You cannot use `indexDetailsKey` with `indexDetailsName`.
`indexDetailsName`	string	Optional. If `indexDetails` is `true`, you can use `indexDetailsName` to filter index details by specifying the index `name`. Only the index name that exactly matches `indexDetailsName` will be returned. If no match is found, `indexDetails` will display statistics for all indexes. Use `getIndexes()` to discover index names. You cannot use `indexDetailsName` with `indexDetailsField`.

To specify just the scale factor, MongoDB supports the legacy format:

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db.collection.stats(<number>)

Returns:	A document that contains statistics on the specified collection. See `collStats` for a breakdown of the returned statistics.

The db.collection.stats() method provides a wrapper around the database command collStats.

Behavior¶

Scaled Sizes¶

Unless otherwise specified by the metric name (such as "bytes currently in the cache"), values related to size are displayed in bytes and can be overridden by scale.

The scale factor rounds the affected size values to whole numbers.

Storage Engine¶

Depending on the storage engine, the data returned may differ. For details on the fields, see output details.

Accuracy after Unexpected Shutdown¶

After an unclean shutdown of a mongod using the Wired Tiger storage engine, count and size statistics reported by db.collection.stats() may be inaccurate.

The amount of drift depends on the number of insert, update, or delete operations performed between the last checkpoint and the unclean shutdown. Checkpoints usually occur every 60 seconds. However, mongod instances running with non-default --syncdelay settings may have more or less frequent checkpoints.

Run validate on each collection on the mongod to restore the correct statistics after an unclean shutdown.

Replica Set Member State Restriction¶

Starting in MongoDB 4.4, to run on a replica set member, collStats operations require the member to be in PRIMARY or SECONDARY state. If the member is in another state, such as STARTUP2, the operation errors.

In previous versions, the operations can also be run when the member is in STARTUP2. However, the operations wait until the member transitions to RECOVERING.

Index Filter Behavior¶

Filtering on indexDetails using either indexDetailsKey or indexDetailsName will only return a single matching index. If no exact match is found, indexDetails will show information on all indexes for the collection.

The indexDetailsKey field takes a document of the following form:

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{ '<string>' : <value>, '<string>' : <value>, ... }

Where <string>> is the field that is indexed and <value> is either the direction of the index, or the special index type such as text or 2dsphere. See index types for the full list of index types.

Unexpected Shutdown and Count¶

For MongoDB instances using the WiredTiger storage engine, after an unclean shutdown, statistics on size and count may off by up to 1000 documents as reported by collStats, dbStats, count. To restore the correct statistics for the collection, run validate on the collection.

In-Progress Indexes¶

Starting in MongoDB 4.2, the db.collection.stats includes information on indexes currently being built. For details, see:

Examples¶

Note

You can find the collection data used for these examples in our primer-dataset.json

Basic Stats Lookup¶

The following operation returns stats on the restaurants collection in the test database:

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db.restaurants.stats()

The operation returns:

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{
   "ns" : "test.restaurants",
   "size" : 7557340,
   "count" : 25359,
   "avgObjSize" : 298,
   "storageSize" : 9670656,
   "freeStorageSize" : 6660096,
   "capped" : false,
   "wiredTiger" : {
         "metadata" : {
            "formatVersion" : 1
         },
         "creationString" : "access_pattern_hint=none,allocation_size=4KB,app_metadata=(formatVersion=1),assert=(commit_timestamp=none,durable_timestamp=none,read_timestamp=none),block_allocation=best,block_compressor=snappy,cache_resident=false,checksum=on,colgroups=,collator=,columns=,dictionary=0,encryption=(keyid=,name=),exclusive=false,extractor=,format=btree,huffman_key=,huffman_value=,ignore_in_memory_cache_size=false,immutable=false,internal_item_max=0,internal_key_max=0,internal_key_truncate=true,internal_page_max=4KB,key_format=q,key_gap=10,leaf_item_max=0,leaf_key_max=0,leaf_page_max=32KB,leaf_value_max=64MB,log=(enabled=true),lsm=(auto_throttle=true,bloom=true,bloom_bit_count=16,bloom_config=,bloom_hash_count=8,bloom_oldest=false,chunk_count_limit=0,chunk_max=5GB,chunk_size=10MB,merge_custom=(prefix=,start_generation=0,suffix=),merge_max=15,merge_min=0),memory_page_image_max=0,memory_page_max=10m,os_cache_dirty_max=0,os_cache_max=0,prefix_compression=false,prefix_compression_min=4,source=,split_deepen_min_child=0,split_deepen_per_child=0,split_pct=90,type=file,value_format=u",
         "type" : "file",
         "uri" : "statistics:table:collection-43-6797839137631957852",
         "LSM" : {
            "bloom filter false positives" : 0,
            "bloom filter hits" : 0,
            "bloom filter misses" : 0,
            "bloom filter pages evicted from cache" : 0,
            "bloom filter pages read into cache" : 0,
            "bloom filters in the LSM tree" : 0,
            "chunks in the LSM tree" : 0,
            "highest merge generation in the LSM tree" : 0,
            "queries that could have benefited from a Bloom filter that did not exist" : 0,
            "sleep for LSM checkpoint throttle" : 0,
            "sleep for LSM merge throttle" : 0,
            "total size of bloom filters" : 0
         },
         "block-manager" : {
            "allocations requiring file extension" : 460,
            "blocks allocated" : 556,
            "blocks freed" : 420,
            "checkpoint size" : 2994176,
            "file allocation unit size" : 4096,
            "file bytes available for reuse" : 6660096,
            "file magic number" : 120897,
            "file major version number" : 1,
            "file size in bytes" : 9670656,
            "minor version number" : 0
         },
         "btree" : {
            "btree checkpoint generation" : 58,
            "column-store fixed-size leaf pages" : 0,
            "column-store internal pages" : 0,
            "column-store variable-size RLE encoded values" : 0,
            "column-store variable-size deleted values" : 0,
            "column-store variable-size leaf pages" : 0,
            "fixed-record size" : 0,
            "maximum internal page key size" : 368,
            "maximum internal page size" : 4096,
            "maximum leaf page key size" : 2867,
            "maximum leaf page size" : 32768,
            "maximum leaf page value size" : 67108864,
            "maximum tree depth" : 3,
            "number of key/value pairs" : 0,
            "overflow pages" : 0,
            "pages rewritten by compaction" : 0,
            "row-store empty values" : 0,
            "row-store internal pages" : 0,
            "row-store leaf pages" : 0
         },
         "cache" : {
            "bytes currently in the cache" : 19401033,
            "bytes dirty in the cache cumulative" : 28415209,
            "bytes read into cache" : 0,
            "bytes written from cache" : 31893695,
            "checkpoint blocked page eviction" : 0,
            "data source pages selected for eviction unable to be evicted" : 0,
            "eviction walk passes of a file" : 0,
            "eviction walk target pages histogram - 0-9" : 0,
            "eviction walk target pages histogram - 10-31" : 0,
            "eviction walk target pages histogram - 128 and higher" : 0,
            "eviction walk target pages histogram - 32-63" : 0,
            "eviction walk target pages histogram - 64-128" : 0,
            "eviction walks abandoned" : 0,
            "eviction walks gave up because they restarted their walk twice" : 0,
            "eviction walks gave up because they saw too many pages and found no candidates" : 0,
            "eviction walks gave up because they saw too many pages and found too few candidates" : 0,
            "eviction walks reached end of tree" : 0,
            "eviction walks started from root of tree" : 0,
            "eviction walks started from saved location in tree" : 0,
            "hazard pointer blocked page eviction" : 0,
            "in-memory page passed criteria to be split" : 4,
            "in-memory page splits" : 2,
            "internal pages evicted" : 0,
            "internal pages split during eviction" : 0,
            "leaf pages split during eviction" : 2,
            "modified pages evicted" : 2,
            "overflow pages read into cache" : 0,
            "page split during eviction deepened the tree" : 0,
            "page written requiring cache overflow records" : 0,
            "pages read into cache" : 0,
            "pages read into cache after truncate" : 1,
            "pages read into cache after truncate in prepare state" : 0,
            "pages read into cache requiring cache overflow entries" : 0,
            "pages requested from the cache" : 76607,
            "pages seen by eviction walk" : 0,
            "pages written from cache" : 552,
            "pages written requiring in-memory restoration" : 0,
            "tracked dirty bytes in the cache" : 0,
            "unmodified pages evicted" : 0
         },
         "cache_walk" : {
            "Average difference between current eviction generation when the page was last considered" : 0,
            "Average on-disk page image size seen" : 0,
            "Average time in cache for pages that have been visited by the eviction server" : 0,
            "Average time in cache for pages that have not been visited by the eviction server" : 0,
            "Clean pages currently in cache" : 0,
            "Current eviction generation" : 0,
            "Dirty pages currently in cache" : 0,
            "Entries in the root page" : 0,
            "Internal pages currently in cache" : 0,
            "Leaf pages currently in cache" : 0,
            "Maximum difference between current eviction generation when the page was last considered" : 0,
            "Maximum page size seen" : 0,
            "Minimum on-disk page image size seen" : 0,
            "Number of pages never visited by eviction server" : 0,
            "On-disk page image sizes smaller than a single allocation unit" : 0,
            "Pages created in memory and never written" : 0,
            "Pages currently queued for eviction" : 0,
            "Pages that could not be queued for eviction" : 0,
            "Refs skipped during cache traversal" : 0,
            "Size of the root page" : 0,
            "Total number of pages currently in cache" : 0
         },
         "compression" : {
            "compressed page maximum internal page size prior to compression" : 4096,
            "compressed page maximum leaf page size prior to compression " : 111392,
            "compressed pages read" : 0,
            "compressed pages written" : 548,
            "page written failed to compress" : 0,
            "page written was too small to compress" : 4
         },
         "cursor" : {
            "bulk loaded cursor insert calls" : 0,
            "cache cursors reuse count" : 74,
            "close calls that result in cache" : 0,
            "create calls" : 4,
            "insert calls" : 50718,
            "insert key and value bytes" : 24500283,
            "modify" : 0,
            "modify key and value bytes affected" : 0,
            "modify value bytes modified" : 0,
            "next calls" : 101747,
            "open cursor count" : 0,
            "operation restarted" : 0,
            "prev calls" : 1,
            "remove calls" : 0,
            "remove key bytes removed" : 0,
            "reserve calls" : 0,
            "reset calls" : 51000,
            "search calls" : 25359,
            "search near calls" : 25485,
            "truncate calls" : 0,
            "update calls" : 0,
            "update key and value bytes" : 0,
            "update value size change" : 0
         },
         "reconciliation" : {
            "dictionary matches" : 0,
            "fast-path pages deleted" : 0,
            "internal page key bytes discarded using suffix compression" : 1077,
            "internal page multi-block writes" : 1,
            "internal-page overflow keys" : 0,
            "leaf page key bytes discarded using prefix compression" : 0,
            "leaf page multi-block writes" : 12,
            "leaf-page overflow keys" : 0,
            "maximum blocks required for a page" : 1,
            "overflow values written" : 0,
            "page checksum matches" : 0,
            "page reconciliation calls" : 80,
            "page reconciliation calls for eviction" : 2,
            "pages deleted" : 0
         },
         "session" : {
            "object compaction" : 0
         },
         "transaction" : {
            "update conflicts" : 0
         }
   },
   "nindexes" : 4,
   "indexBuilds" : [ ],       // Available starting in MongoDB 4.2
   "totalIndexSize" : 704512,
   "totalSize" : 10375168,    // Available starting in MongoDB 4.4
   "indexSizes" : {
      "_id_" : 241664,
      "cuisine_1" : 147456,
      "borough_1_cuisine_1" : 159744,
      "borough_1_address.zipcode_1" : 155648
   },
   "scaleFactor" : 1,        // Available starting in MongoDB 4.2
   "ok" : 1
}

As stats was not give a scale parameter, all size values are in bytes.

Stats Lookup With Scale¶

The following operation changes the scale of data from bytes to kilobytes by specifying a scale of 1024:

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db.restaurants.stats( { scale : 1024 } )

The operation returns:

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{
   "ns" : "test.restaurants",
   "size" : 7380,
   "count" : 25359,
   "avgObjSize" : 298,
   "storageSize" : 9444,
   "freeStorageSize" : 6504,
   "capped" : false,
   "wiredTiger" : {
      ...
   },
   "nindexes" : 4,
   "indexBuilds" : [ ],      // Available starting in MongoDB 4.2
   "totalIndexSize" : 688,
   "totalSize" : 10132,      // Available starting in MongoDB 4.4
   "indexSizes" : {
      "_id_" : 236,
      "cuisine_1" : 144,
      "borough_1_cuisine_1" : 156,
      "borough_1_address.zipcode_1" : 152
   },
   "scaleFactor" : 1024,     // Available starting in MongoDB 4.2
   "ok" : 1
}

Statistics Lookup With Index Details¶

The following operation creates an indexDetails document that contains information related to each of the indexes within the collection:

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db.restaurants.stats( { indexDetails : true } )

The operation returns:

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{
   "ns" : "test.restaurants",
   "size" : 7557340,
   "count" : 25359,
   "avgObjSize" : 298,
   "storageSize" : 9670656,
   "freeStorageSize" : 6660096,
   "capped" : false,
   "wiredTiger" : {
   ...
   },
   "nindexes" : 4,
   "indexDetails" : {
      "_id_" : {
         "metadata" : {
            "formatVersion" : 8
         },
         "creationString" : "access_pattern_hint=none,allocation_size=4KB,app_metadata=(formatVersion=8),assert=(commit_timestamp=none,durable_timestamp=none,read_timestamp=none),block_allocation=best,block_compressor=,cache_resident=false,checksum=on,colgroups=,collator=,columns=,dictionary=0,encryption=(keyid=,name=),exclusive=false,extractor=,format=btree,huffman_key=,huffman_value=,ignore_in_memory_cache_size=false,immutable=false,internal_item_max=0,internal_key_max=0,internal_key_truncate=true,internal_page_max=16k,key_format=u,key_gap=10,leaf_item_max=0,leaf_key_max=0,leaf_page_max=16k,leaf_value_max=0,log=(enabled=true),lsm=(auto_throttle=true,bloom=true,bloom_bit_count=16,bloom_config=,bloom_hash_count=8,bloom_oldest=false,chunk_count_limit=0,chunk_max=5GB,chunk_size=10MB,merge_custom=(prefix=,start_generation=0,suffix=),merge_max=15,merge_min=0),memory_page_image_max=0,memory_page_max=5MB,os_cache_dirty_max=0,os_cache_max=0,prefix_compression=true,prefix_compression_min=4,source=,split_deepen_min_child=0,split_deepen_per_child=0,split_pct=90,type=file,value_format=u",
         "type" : "file",
         "uri" : "statistics:table:index-44-6797839137631957852",
         "LSM" : {
         ...
         },
         "block-manager" : {
         ...
         },
         "btree" : {
         ...
         },
         "cache" : {
         ...
         },
         "cache_walk" : {
         ...
         },
         "compression" : {
         ...
         },
         "cursor" : {
         ...
         },
         "reconciliation" : {
         ...
         },
         "session" : {
         ...
         },
         "transaction" : {
         ...
         }
      },
      "cuisine_1" : {
         ...
      },
      "borough_1_cuisine_1" : {
         ...
      },
      "borough_1_address.zipcode_1" : {
         ...
   },
   "indexBuilds" : [ ],         // Available starting in MongoDB 4.2
   "totalIndexSize" : 704512,
   "totalSize" : 10375168,      // Available starting in MongoDB 4.4
   "indexSizes" : {
      "_id_" : 241664,
      "cuisine_1" : 147456,
      "borough_1_cuisine_1" : 159744,
      "borough_1_address.zipcode_1" : 155648
   },
   "scaleFactor" : 1,          // Available starting in MongoDB 4.2
   "ok" : 1
}

Statistics Lookup With Filtered Index Details¶

To filter the indexes in the indexDetails field, you can either specify the index keys using the indexDetailsKey option or specify the index name using the indexDetailsName. To discover index keys and names for the collection, use db.collection.getIndexes().

Given the following index:

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{
   "ns" : "test.restaurants",
   "v" : 1,
   "key" : {
      "borough" : 1,
      "cuisine" : 1
   },
   "name" : "borough_1_cuisine_1"
}

The following operation filters the indexDetails document to a single index as defined by the indexDetailsKey document.

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db.restaurants.stats(
   {
      'indexDetails' : true,
      'indexDetailsKey' :
      {
         'borough' : 1,
         'cuisine' : 1
      }
   }
)

The following operation filters the indexDetails document to a single index as defined by the indexDetailsName document.

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db.restaurants.stats(
   {
      'indexDetails' : true,
      'indexDetailsName' : 'borough_1_cuisine_1'
   }
)

Both operations will return the same output:

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{
   "ns" : "test.restaurants",
   "size" : 7557340,
   "count" : 25359,
   "avgObjSize" : 298,
   "storageSize" : 9670656,
   "freeStorageSize" : 6660096,
   "capped" : false,
   "wiredTiger" : {
      ...
   },
   "nindexes" : 4,
   "indexDetails" : {
      "borough_1_cuisine_1" : {
         "metadata" : {
            "formatVersion" : 8
         },
         "LSM" : {
            ...
         },
         "block-manager" : {
            ...
         },
         "btree" : {
            ...
         },
         "cache" : {
            ...
         },
         "cache_walk" : {
            ...
         },
         "compression" : {
            ...
         },
         "cursor" : {
            ...
         },
         "reconciliation" : {
            ...
         },
         "session" : {
            ...
         },
         "transaction" : {
            ...
         }
      }
   },
   "indexBuilds" : [ ],          // Available starting in MongoDB 4.2
   "totalIndexSize" : 704512,
   "totalSize" : 10375168,       // Available starting in MongoDB 4.4
   "indexSizes" : {
      "_id_" : 241664,
      "cuisine_1" : 147456,
      "borough_1_cuisine_1" : 159744,
      "borough_1_address.zipcode_1" : 155648
   },
   "scaleFactor" : 1,            // Available starting in MongoDB 4.2
   "ok" : 1
}

For explanation of the output, see output details.