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collStats

Definition

collStats

The collStats command returns a variety of storage statistics for a given collection.

To run collStats, use the db.runCommand( { <command> } ) method.

The collStats command has the following syntax:

{
   collStats: <string>,
   scale: <int>,
   verbose: <boolean>
}

The command takes the following fields:

Field Type Description
collStats string

The name of the target collection.

If the collection does not exist, collStats returns an error message.

scale int

Optional. The scale used in the output to display the sizes of items. By default, output displays sizes in bytes. To display kilobytes rather than bytes, specify a scale value of 1024.

The scale factor rounds values to whole numbers.

verbose boolean

Optional. When true, collStats increases reporting for the MMAPv1 Storage Engine.

Defaults to false.

Behavior

Accuracy after Unexpected Shutdown

After an unclean shutdown of a mongod using the Wired Tiger storage engine, size statistics reported by collStats 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 to restore the correct statistics after an unclean shutdown.

Example

The following operation runs the collStats command on the restaurants collection, specifying a scale of 1024 bytes:

db.runCommand( { collStats : "restaurants", scale: 1024 } )

The following document provides a representation of the collStats output. Depending on the configuration of your collection and the storage engine, the output fields may vary.

{
  "ns" : <string>,
  "size" : <number>,
  "count" : <number>,
  "avgObjSize" : <number>,
  "storageSize" : <number>,
  "capped" : <boolean>,
  "max" : <number>,
  "maxSize" :  <number>,
  "wiredTiger" : {
     "metadata" : {
        "formatVersion" : <num>
     },
     "creationString" : <string>
     "type" :  <string>,
     "uri" :  <string>,
     "LSM" : {
        "bloom filters in the LSM tree" : <number>,
        "bloom filter false positives" : <number>,
        "bloom filter hits" : <number>,
        "bloom filter misses" : <number>,
        "bloom filter pages evicted from cache" : <number>,
        "bloom filter pages read into cache" : <number>,
        "total size of bloom filters" : <number>,
        "sleep for LSM checkpoint throttle" : <number>,
        "chunks in the LSM tree" : <number>,
        "highest merge generation in the LSM tree" : <number>,
        "queries that could have benefited from a Bloom filter that did not exist" : <number>,
        "sleep for LSM merge throttle" : <number>
     },
     "block-manager" : {
         "allocations requiring file extension" : <number>,
         "blocks allocated" : <number>,
         "blocks freed" : <number>,
         "checkpoint size" : <number>,
         "file allocation unit size" : <number>,
         "file bytes available for reuse" : <number>,
         "file magic number" : <number>,
         "file major version number" : <number>,
         "file size in bytes" : <number>,
         "minor version number" : <number>
     },
     "btree" : {
         "btree checkpoint generation" : <number>,
         "column-store fixed-size leaf pages" : <number>,
         "column-store internal pages" : <number>,
         "column-store variable-size RLE encoded values" : <number>,
         "column-store variable-size deleted values" : <number>,
         "column-store variable-size leaf pages" : <number>,
         "fixed-record size" : <number>,
         "maximum internal page key size" : <number>,
         "maximum internal page size" : <number>,
         "maximum leaf page key size" : <number>,
         "maximum leaf page size" : <number>,
         "maximum leaf page value size" : <number>,
         "maximum tree depth" : <number>,
         "number of key/value pairs" : <number>,
         "overflow pages" : <number>,
         "pages rewritten by compaction" : <number>,
         "row-store internal pages" : <number>,
         "row-store leaf pages" : <number>
     },
     "cache" : {
        "bytes currently in the cache" : <number>,
        "bytes dirty in the cache cumulative" : <number>,
        "bytes read into cache" : <number>,
        "bytes written from cache" : <number>,
        "checkpoint blocked page eviction" : <number>,
        "data source pages selected for eviction unable to be evicted" : <number>,
        "eviction walk passes of a file" : <number>,
        "eviction walk target pages histogram - 0-9" : <number>,
        "eviction walk target pages histogram - 10-31" : <number>,
        "eviction walk target pages histogram - 128 and higher" : <number>,
        "eviction walk target pages histogram - 32-63" : <number>,
        "eviction walk target pages histogram - 64-128" : <number>,
        "eviction walks abandoned" : <number>,
        "eviction walks gave up because they restarted their walk twice" : <number>,
        "eviction walks gave up because they saw too many pages and found no candidates" : <number>,
        "eviction walks gave up because they saw too many pages and found too few candidates" : <number>,
        "eviction walks reached end of tree" : <number>,
        "eviction walks started from root of tree" : <number>,
        "eviction walks started from saved location in tree" : <number>,
        "hazard pointer blocked page eviction" : <number>,
        "in-memory page passed criteria to be split" : <number>,
        "in-memory page splits" : <number>,
        "internal pages evicted" : <number>,
        "internal pages split during eviction" : <number>,
        "leaf pages split during eviction" : <number>,
        "modified pages evicted" : <number>,
        "overflow pages read into cache" : <number>,
        "page split during eviction deepened the tree" : <number>,
        "page written requiring cache overflow records" : <number>,
        "pages read into cache" : <number>,
        "pages read into cache after truncate" : <number>,
        "pages read into cache after truncate in prepare state" : <number>,
        "pages read into cache requiring cache overflow entries" : <number>,
        "pages requested from the cache" : <number>,
        "pages seen by eviction walk" : <number>,
        "pages written from cache" : <number>,
        "pages written requiring in-memory restoration" : <number>,
        "tracked dirty bytes in the cache" : <number>,
        "unmodified pages evicted" : <number>
     },
     "cache_walk" : {
        "Average difference between current eviction generation when the page was last considered" : <number>,
        "Average on-disk page image size seen" : <number>,
        "Average time in cache for pages that have been visited by the eviction server" : <number>,
        "Average time in cache for pages that have not been visited by the eviction server" : <number>,
        "Clean pages currently in cache" : <number>,
        "Current eviction generation" : <number>,
        "Dirty pages currently in cache" : <number>,
        "Entries in the root page" : <number>,
        "Internal pages currently in cache" : <number>,
        "Leaf pages currently in cache" : <number>,
        "Maximum difference between current eviction generation when the page was last considered" : <number>,
        "Maximum page size seen" : <number>,
        "Minimum on-disk page image size seen" : <number>,
        "Number of pages never visited by eviction server" : <number>,
        "On-disk page image sizes smaller than a single allocation unit" : <number>,
        "Pages created in memory and never written" : <number>,
        "Pages currently queued for eviction" : <number>,
        "Pages that could not be queued for eviction" : <number>,
        "Refs skipped during cache traversal" : <number>,
        "Size of the root page" : <number>,
        "Total number of pages currently in cache" : <number>
     },
     "compression" : {
        "compressed pages read" : <number>,
        "compressed pages written" : <number>,
        "page written failed to compress" : <number>,
        "page written was too small to compress" : 1
     },
     "cursor" : {
        "bulk-loaded cursor-insert calls" : <number>,
        "close calls that result in cache" : <number>,
        "create calls" : <number>,
        "cursor operation restarted" : <number>,
        "cursor-insert key and value bytes inserted" : <number>,
        "cursor-remove key bytes removed" : <number>,
        "cursor-update value bytes updated" : <number>,
        "cursors reused from cache" : <number>,
        "insert calls" : <number>,
        "modify calls" : <number>,
        "next calls" : <number>,
        "open cursor count" : <number>,
        "prev calls" : <number>,
        "remove calls" : <number>,
        "reserve calls" : <number>,
        "reset calls" : <number>,
        "search calls" : <number>,
        "search near calls" : <number>,
        "truncate calls" : <number>,
        "update calls" : <number>
     },
     "reconciliation" : {
        "dictionary matches" : <number>,
        "fast-path pages deleted" : <number>,
        "internal page key bytes discarded using suffix compression" : <number>,
        "internal page multi-block writes" : <number>,
        "internal-page overflow keys" : <number>,
        "leaf page key bytes discarded using prefix compression" : <number>,
        "leaf page multi-block writes" : <number>,
        "leaf-page overflow keys" : <number>,
        "maximum blocks required for a page" : <number>,
        "overflow values written" : <number>,
        "page checksum matches" : <number>,
        "page reconciliation calls" : <number>,
        "page reconciliation calls for eviction" : <number>,
        "pages deleted" : <number>
     },
     "session" : {
        "object compaction" : <number>,
     },
     "transaction" : {
        "update conflicts" : <number>
     }
  },
  "nindexes" : <number>,
  "totalIndexSize" : <number>,
  "indexSizes" : {
          "_id_" : <number>,
          "username" : <number>
  },
  // ...
  "ok" : <number>
}

Output

collStats.ns

The namespace of the current collection, which follows the format [database].[collection].

collStats.size

The total uncompressed size in memory of all records in a collection. The size does not include the size of any indexes associated with the collection, which the totalIndexSize field reports.

For the deprecated MMAPv1 storage engine, size includes the record’s padding but not the record header, which is 16 bytes per record.

The scale argument affects size. Data compression does not affect this value.

collStats.count

The number of objects or documents in this collection.

collStats.avgObjSize

The average size of an object in the collection (plus any padding for MMAPv1). The scale argument does not affect this value.

collStats.storageSize

The total amount of storage allocated to this collection for document storage. The scale argument affects this value.

If collection data is compressed (which is the default for WiredTiger), the storage size reflects the compressed size and may be smaller than the value for collStats.size.

storageSize does not include index size. See totalIndexSize for index sizing.

For MMAPv1, storageSize will not decrease as you remove or shrink documents.

collStats.numExtents

The total number of contiguously allocated data file regions. Only present when using the MMAPv1 storage engine.

collStats.nindexes

The number of indexes on the collection. All collections have at least one index on the _id field.

collStats.lastExtentSize

The size of the last extent allocated. The scale argument affects this value. Only present when using the mmapv1 storage engine.

collStats.paddingFactor

Deprecated since version 3.0.0: paddingFactor is no longer used in 3.0.0, and remains hard coded to 1.0 for compatibility only.

paddingFactor only appears when using the mmapv1 storage engine.

collStats.userFlags

A number that indicates the user-set flags on the collection. userFlags only appears when using the mmapv1 storage engine.

Changed in version 3.0.0: userFlags reports on the usePowerOf2Sizes and the noPadding flags.

Note

MongoDB 3.0 ignores the usePowerOf2Sizes flag. See collMod and db.createCollection() for more information.

collStats.totalIndexSize

The total size of all indexes. The scale argument affects this value.

If an index uses prefix compression (which is the default for WiredTiger), the returned size reflects the compressed size for any such indexes when calculating the total.

collStats.indexSizes

This field specifies the key and size of every existing index on the collection. The scale argument affects this value.

If an index uses prefix compression (which is the default for WiredTiger), the returned size reflects the compressed size.

collStats.capped

This field will be “true” if the collection is capped.

collStats.max

Shows the maximum number of documents that may be present in a capped collection.

collStats.maxSize

Shows the maximum size of a capped collection.

collStats.wiredTiger

New in version 3.0.0.

wiredTiger only appears when using the WiredTiger storage engine.

This document contains data reported directly by the WiredTiger engine and other data for internal diagnostic use.

collStats.indexDetails

New in version 3.0.0.

A document that reports data from the WiredTiger storage engine for each index in the collection. Other storage engines will return an empty document.

The fields in this document are the names of the indexes, while the values themselves are documents that contain statistics for the index provided by the storage engine. These statistics are for internal diagnostic use.

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