接触过MySQL的同学应该知道，表进行批量的delete操作之后，数据盘空间并不会马上释放，innodb只是把删除的行对应的数据块做下标记，下次使用时候会优先使用。
而MongoDB也有类似的情况，批量remove文档之后，磁盘空间并不会释放，我们可以使用compact进行碎片整理。
注意事项
- 实例的存储引擎为WiredTiger。
- 该操作会导致集合所属的数据库被锁定，且该数据库的读写操作将被阻塞，务必在业务低峰期操作。
单机或者副本集
查看集合基本信息
> db.usertable.stats().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:ycsb1/collection-2--8436275121761636149",
"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" : 49752,
"blocks allocated" : 49774,
"blocks freed" : 49761,
"checkpoint size" : 0,
"file allocation unit size" : 4096,
"file bytes available for reuse" : 1420492800,
"file magic number" : 120897,
"file major version number" : 1,
"file size in bytes" : 1420505088,
"minor version number" : 0
},
"btree" : {
"btree checkpoint generation" : 27,
"btree clean tree checkpoint expiration time" : NumberLong("9223372036854775807"),
"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" : 4,
"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" : 24555798,
"bytes dirty in the cache cumulative" : 1563881912,
"bytes read into cache" : 425821233,
"bytes written from cache" : 1417712072,
"checkpoint blocked page eviction" : 53,
"data source pages selected for eviction unable to be evicted" : 81,
"eviction walk passes of a file" : 2727,
"eviction walk target pages histogram - 0-9" : 164,
"eviction walk target pages histogram - 10-31" : 336,
"eviction walk target pages histogram - 128 and higher" : 0,
"eviction walk target pages histogram - 32-63" : 466,
"eviction walk target pages histogram - 64-128" : 1761,
"eviction walks abandoned" : 53,
"eviction walks gave up because they restarted their walk twice" : 5,
"eviction walks gave up because they saw too many pages and found no candidates" : 124,
"eviction walks gave up because they saw too many pages and found too few candidates" : 60,
"eviction walks reached end of tree" : 175,
"eviction walks started from root of tree" : 243,
"eviction walks started from saved location in tree" : 2484,
"hazard pointer blocked page eviction" : 9,
"in-memory page passed criteria to be split" : 356,
"in-memory page splits" : 172,
"internal pages evicted" : 404,
"internal pages split during eviction" : 4,
"leaf pages split during eviction" : 177,
"modified pages evicted" : 48451,
"overflow pages read into cache" : 0,
"page split during eviction deepened the tree" : 1,
"page written requiring cache overflow records" : 0,
"pages read into cache" : 14676,
"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" : 7689354,
"pages seen by eviction walk" : 1194026,
"pages written from cache" : 49765,
"pages written requiring in-memory restoration" : 2,
"tracked dirty bytes in the cache" : 0,
"unmodified pages evicted" : 14256
},
"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 " : 32768,
"compressed pages read" : 88,
"compressed pages written" : 105,
"page written failed to compress" : 49176,
"page written was too small to compress" : 484
},
"cursor" : {
"bulk loaded cursor insert calls" : 0,
"cache cursors reuse count" : 981,
"close calls that result in cache" : 0,
"create calls" : 5,
"insert calls" : 982334,
"insert key and value bytes" : 1399137825,
"modify" : 0,
"modify key and value bytes affected" : 0,
"modify value bytes modified" : 0,
"next calls" : 990110,
"open cursor count" : 0,
"operation restarted" : 0,
"prev calls" : 2,
"remove calls" : 982334,
"remove key bytes removed" : 3846971,
"reserve calls" : 0,
"reset calls" : 2971484,
"search calls" : 1964668,
"search near calls" : 990109,
"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" : 99217,
"internal page multi-block writes" : 9,
"internal-page overflow keys" : 0,
"leaf page key bytes discarded using prefix compression" : 0,
"leaf page multi-block writes" : 179,
"leaf-page overflow keys" : 0,
"maximum blocks required for a page" : 1,
"overflow values written" : 0,
"page checksum matches" : 413,
"page reconciliation calls" : 50044,
"page reconciliation calls for eviction" : 47098,
"pages deleted" : 49020
},
"session" : {
"object compaction" : 0
},
"transaction" : {
"update conflicts" : 0
}
}
删除文档
> use ycsb1
switched to db ycsb1
>
> db.usertable.remove({})
WriteResult({ "nRemoved" : 982334 })
> db.usertable.count()
0可以看到集合已经清空。
查看磁盘占用
找到数据目录
[root@mongodb data]# du -sm ycsb1/
1405 ycsb1/碎片整理
> db.runCommand({compact:"usertable",force:true})
{ "ok" : 1 }查看磁盘占用
[root@mongodb data]# du -sm ycsb1/
1 ycsb1/
可以看到磁盘空间已经释放。
接下来登录secondary节点进行同样的操作。
分片集
查看分片信息
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("60545017224c766911a9c440")
}
shards:
{ "_id" : "hdshard1", "host" : "hdshard1/172.16.254.136:40001,172.16.254.137:40001,172.16.254.138:40001", "state" : 1 }
{ "_id" : "hdshard2", "host" : "hdshard2/172.16.254.136:40002,172.16.254.137:40002,172.16.254.138:40002", "state" : 1 }
{ "_id" : "hdshard3", "host" : "hdshard3/172.16.254.136:40003,172.16.254.137:40003,172.16.254.138:40003", "state" : 1 }
active mongoses:
"4.2.12" : 3
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
52 : Success
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
hdshard1 342
hdshard2 341
hdshard3 341
too many chunks to print, use verbose if you want to force print
{ "_id" : "db1", "primary" : "hdshard3", "partitioned" : true, "version" : { "uuid" : UUID("71bb472c-7896-4a31-a77c-e3aaf723be3c"), "lastMod" : 1 } }
{ "_id" : "db2", "primary" : "hdshard2", "partitioned" : false, "version" : { "uuid" : UUID("add90941-a8b1-4c40-94e9-9ccc38d73096"), "lastMod" : 2 } }
{ "_id" : "db3", "primary" : "hdshard3", "partitioned" : false, "version" : { "uuid" : UUID("f0278f73-d999-453f-8739-eac30a8bcf9b"), "lastMod" : 1 } }
{ "_id" : "recommend", "primary" : "hdshard1", "partitioned" : true, "version" : { "uuid" : UUID("cb833b8e-cc4f-4c52-83c3-719aa383bac4"), "lastMod" : 1 } }
recommend.rcmd_1_min_tag_mei_rong
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
hdshard1 2
hdshard2 3
hdshard3 3
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : NumberLong("-6701866976688134138") } on : hdshard3 Timestamp(9, 0)
{ "_id" : NumberLong("-6701866976688134138") } -->> { "_id" : NumberLong("-4163240026901542572") } on : hdshard3 Timestamp(3, 0)
{ "_id" : NumberLong("-4163240026901542572") } -->> { "_id" : NumberLong("-1616330844721205691") } on : hdshard2 Timestamp(7, 1)
{ "_id" : NumberLong("-1616330844721205691") } -->> { "_id" : NumberLong("909129560750995399") } on : hdshard3 Timestamp(5, 0)
{ "_id" : NumberLong("909129560750995399") } -->> { "_id" : NumberLong("3449289120186727718") } on : hdshard2 Timestamp(6, 0)
{ "_id" : NumberLong("3449289120186727718") } -->> { "_id" : NumberLong("5980358241733552715") } on : hdshard2 Timestamp(10, 0)
{ "_id" : NumberLong("5980358241733552715") } -->> { "_id" : NumberLong("8520801504243263436") } on : hdshard1 Timestamp(8, 1)
{ "_id" : NumberLong("8520801504243263436") } -->> { "_id" : { "$maxKey" : 1 } } on : hdshard1 Timestamp(1, 7)
recommend.rcmd_1_tag_li_liao
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
hdshard1 36
hdshard2 35
hdshard3 36
too many chunks to print, use verbose if you want to force print
{ "_id" : "ycsb", "primary" : "hdshard2", "partitioned" : true, "version" : { "uuid" : UUID("df4f702f-bb9f-477c-a327-c4b4f28ccf8f"), "lastMod" : 1 } }
ycsb.usertable
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
hdshard1 11
hdshard2 11
hdshard3 11
too many chunks to print, use verbose if you want to force print
{ "_id" : "ycsb1", "primary" : "hdshard2", "partitioned" : true, "version" : { "uuid" : UUID("c7e227d8-0739-41c7-b47e-9d36065454d3"), "lastMod" : 1 } }
ycsb1.usertable
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
hdshard1 8
hdshard2 8
hdshard3 9
too many chunks to print, use verbose if you want to force print可以看到ycsb1库的主分片节点是hdshard2。
删除文档
mongos> use ycsb1
switched to db ycsb1
mongos> show collections
usertable
mongos> db.usertable.remove({})
WriteResult({ "nRemoved" : 982334 })
mongos> db.usertable.count()
0
查看磁盘
登录分片所在服务器，进入数据目录
[mongodb@mongo7 shard2]$ du -sm ycsb1
1448 ycsb1碎片整理
hdshard2:PRIMARY> db.runCommand({compact:"usertable",force:true})
{
"ok" : 1,
"$gleStats" : {
"lastOpTime" : Timestamp(0, 0),
"electionId" : ObjectId("7fffffff0000000000000030")
},
"lastCommittedOpTime" : Timestamp(1619505175, 4),
"$configServerState" : {
"opTime" : {
"ts" : Timestamp(1619505181, 1),
"t" : NumberLong(22)
}
},
"$clusterTime" : {
"clusterTime" : Timestamp(1619505181, 1),
"signature" : {
"hash" : BinData(0,"zcROSPOVYMxzJouTvGAZ4S0Ddh4="),
"keyId" : NumberLong("6941260985399246879")
}
},
"operationTime" : Timestamp(1619505175, 4)
}
查看磁盘
[mongodb@mongo7 shard2]$ du -sm ycsb1
1 ycsb1
可以看到磁盘空间已经释放。
接下来登录secondary节点重复上述操作。
说明
- 如果新数据写入较快，可以不进行compact，这些碎片会很快被使用。
- 如果使用db.collection.drop()进行集合删除，无需进行碎片整理。
- 如果涉及副本集，需在primary节点和secondary节点进行同样的操作，compact不会传递给secondary节点。