概述

使用MongoDB的过程中，发现会出现磁盘空间爆满的问题，因此简单调研得到此文。

查询版本：db.version();

获取全量集合名：db.getCollectionNames();

统计

在Mongodb中有两个和stats相关的方法：db.stats()和db.collection.stats()。

db.stats()

db.stats()返回整个数据库的基本情况，可以传入一个number类型参数，它会将数据按指定的倍数去显示数据，如db.stats(1024)则按kb显示数据，默认按byte显示：

[
  {
    "avgObjSize": 375.1006008728961,
    "collections": 676,
    "dataSize": 10408153436,
    "db": "ai_cbd_iview_api",
    "indexSize": 387710976,
    "indexes": 1349,
    "numExtents": 0,
    "objects": 27747632,
    "ok": 1,
    "storageSize": 3219529728,
    "views": 0
  }
]

解读：

• db：数据库
• collections：数据库有多少个集合；可通过运行show collections查看当前数据库具体有哪些collection
• objects：当前数据库所有collection总共有多少行数据。显示的数据是一个估计值，并不是非常精确
• avgObjSize：每行数据的大小，估计值，单位bytes
• dataSize：当前数据库所有数据的总大小，不是指占有磁盘大小。单位bytes
• storageSize：当前数据库占有磁盘大小，单位bytes，因为mongodb有预分配空间机制，为了防止当有大量数据插入时对磁盘的压力，因此会事先多分配磁盘空间
• numExtents：连续分配的数据块
• indexes：索引个数
• indexSize：索引占用空间大小
• nsSizeMB：命名空间文件大小

db[''].stats()

查询某个集合统计信息：db['tab_f02742bc4568a7b92b85a0054e4c6836'].stats();，输出：

[
  {
    "avgObjSize": 459,
    "capped": false,
    "count": 2090003,
    "indexSizes": {
      "_id_": 20877312,
      "iview_mongo_index_1": 7118848
    },
    "nindexes": 2,
    "ns": "ai_cbd_iview_api.tab_0bb1fb66b4fd3927b4679e8499d9f88e",
    "ok": 1,
    "size": 959734617,
    "storageSize": 424046592,
    "totalIndexSize": 27996160,
    "wiredTiger": {
      "metadata": {
        "formatVersion": 1
      },
      "creationString": "access_pattern_hint=none,allocation_size=4KB,app_metadata=(formatVersion=1),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_max=15,merge_min=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:ai_cbd_iview_api/collection-30358-6087677533101142803",
      "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": 34827,
        "blocks allocated": 34992,
        "blocks freed": 236,
        "checkpoint size": 423632896,
        "file allocation unit size": 4096,
        "file bytes available for reuse": 397312,
        "file magic number": 120897,
        "file major version number": 1,
        "file size in bytes": 424046592,
        "minor version number": 0
      },
      "btree": {
        "btree checkpoint generation": 194049,
        "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 internal pages": 0,
        "row-store leaf pages": 0
      },
      "cache": {
        "bytes currently in the cache": 237681481,
        "bytes read into cache": 28369,
        "bytes written from cache": 979663693,
        "checkpoint blocked page eviction": 0,
        "data source pages selected for eviction unable to be evicted": 8,
        "hazard pointer blocked page eviction": 0,
        "in-memory page passed criteria to be split": 278,
        "in-memory page splits": 131,
        "internal pages evicted": 0,
        "internal pages split during eviction": 2,
        "leaf pages split during eviction": 105,
        "modified pages evicted": 105,
        "overflow pages read into cache": 0,
        "overflow values cached in memory": 0,
        "page split during eviction deepened the tree": 1,
        "page written requiring lookaside records": 0,
        "pages read into cache": 1,
        "pages read into cache requiring lookaside entries": 0,
        "pages requested from the cache": 2090203,
        "pages written from cache": 34969,
        "pages written requiring in-memory restoration": 0,
        "tracked dirty bytes in the cache": 0,
        "unmodified pages evicted": 264
      },
      "cache_walk": {
        "Average difference between current eviction generation when the page was last considered": 0,
        "Average on-disk page image size seen": 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,
        "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 pages read": 1,
        "compressed pages written": 34475,
        "page written failed to compress": 0,
        "page written was too small to compress": 494,
        "raw compression call failed, additional data available": 0,
        "raw compression call failed, no additional data available": 0,
        "raw compression call succeeded": 0
      },
      "cursor": {
        "bulk-loaded cursor-insert calls": 0,
        "create calls": 7,
        "cursor-insert key and value bytes inserted": 968012264,
        "cursor-remove key bytes removed": 0,
        "cursor-update value bytes updated": 0,
        "insert calls": 2090003,
        "next calls": 2,
        "prev calls": 2,
        "remove calls": 0,
        "reset calls": 33445,
        "restarted searches": 0,
        "search calls": 0,
        "search near calls": 0,
        "truncate calls": 0,
        "update calls": 0
      },
      "reconciliation": {
        "dictionary matches": 0,
        "fast-path pages deleted": 0,
        "internal page key bytes discarded using suffix compression": 70902,
        "internal page multi-block writes": 17,
        "internal-page overflow keys": 0,
        "leaf page key bytes discarded using prefix compression": 0,
        "leaf page multi-block writes": 137,
        "leaf-page overflow keys": 0,
        "maximum blocks required for a page": 62,
        "overflow values written": 0,
        "page checksum matches": 1593,
        "page reconciliation calls": 365,
        "page reconciliation calls for eviction": 1,
        "pages deleted": 2
      },
      "session": {
        "object compaction": 0,
        "open cursor count": 0
      },
      "transaction": {
        "update conflicts": 0
      }
    }
  }
]

解读：

• ns：命名空间，集合名称
• size：集合大小
• count：集合中的文档总数
• avgObjSize：每个obj的大小
• storageSize：分配的存储空间，当删除集合中的文档时，此值不会降低
• capped：是否固定集合
• wiredTiger：wiredTiger储存引擎相关信息
• nindexes：索引数量
• totalIndexSize：索引占用磁盘大小
• indexSizes: 集合索引列表及每个索引占用大小

统计集合大小并降序

可以直接在DataGrip 2021.1.2执行的JS代码，关于DataGrip连接MongoDB数据源的，可以参考DataGrip连接MongoDB及CRUD操作

var sizeArray = [];
// Find statistics of every collection and add to an array
db.getCollectionNames().forEach(function(cName) {
    sizeArray.push(db[cName].stats());
});
// Sort the stats array by size. The field 'size' is used
sizeArray = sizeArray.sort(function(a, b) { return b['size'] - a['size']; });
// Print output in Mb
for (var stat in sizeArray) {
    print(sizeArray[stat]['ns'] + ": count=" + sizeArray[stat]['count']
    + ": " + (sizeArray[stat]['size']/(1024 * 1024)).toFixed(2) + " Mb");
}

tables = db.getCollectionNames();
tables.forEach( function (item) { 
    stats=db.runCommand({collStats:item});
    sizeGB = stats.storageSize/1024/1024/1024;
    prettyGB = Math.round(sizeGB)+ 'GB';
    print(item, prettyGB)
})

统计集合索引大小并降序

var sizeMap = {}
// Iterate through every collection
db.getCollectionNames().forEach(function(cName) {
   indexes = db[cName].stats().indexSizes
   // Now iterate through every index of the current collection
   // We create a map here with key as combination of collection name and index name
   for (i in indexes) sizeMap[cName + " - " + i] = indexes[i];
});
 
var sizeArray = [];
// Map is converted to an array each element of which is a two member array
// This inner arrary contains the collection+index name key and the size itself
for (key in sizeMap) sizeArray.push([key, sizeMap[key]])
// Now sort outer array using the second column of inner array
var sizeArray = sizeArray.sort(function(a, b) {return b[1] - a[1]})
// Print list of index size in sorted form
for (x in sizeArray) print( sizeArray[x][0] + ": " + (sizeArray[x][1]/1024).toFixed(2) +" kb");

清理冗余空间

// primary
db.runCommand({compact:'flow_down_stream_info',force:true})
// secondary
db.runCommand({compact:'flow_down_stream_info'})

建议先在从库上运行，观察没问题后再在primary上运行。
不建议使用repairDatabase()命令，有可能造成数据损坏

Just to clarify, please be careful about using repairDatabase on a replica set node. repairDatabase is meant to be used to salvage readable data i.e. after a disk corruption, so it can remove unreadable data and let MongoDB start in the face of disk corruption.
If this node has an undetected disk corruption and you run repairDatabase on it, this could lead into that particular node having a different data content vs. the other node as a result of repairDatabase. Since MongoDB assumes all nodes in a replica set contains identical data, this could lead to crashes and hard to diagnose problems. Due to its nature, this issue could stay dormant for a long time, and suddenly manifest itself with a vengeance, seemingly without any apparent reason.
WiredTiger will eventually reuse the empty spaces with new data, and the periodic checkpointing that WiredTiger does could potentially release space to the OS without any intervention on your part.
If you really need to give space back to the OS, then an initial sync is the safest choice if you have a replica set. On a standalone, dump/restore will achieve the same result. Otherwise, compact is the safer choice vs. repairDatabase. Please backup your data before doing any of these, since in my opinion this would qualify as a major maintenance

参考

how-to-get-sorted-list-of-collection-and-index-sizes-in-a-mongodb-database
MongoDB / WiredTiger: reduce storage size after deleting properties from documents
https://blog.csdn.net/yanxiaojia521/article/details/122565291