要将现有集合转换为上限，请使用convertToCapped。让我们创建一个包含文档的集合-
> db.demo260.insertOne({"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e47b1181627c0c63e7dba9b")
}
> db.demo260.insertOne({"Name":"Bob"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e47b11c1627c0c63e7dba9c")
}
> db.demo260.insertOne({"Name":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e47b11f1627c0c63e7dba9d")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo260.find();
这将产生以下输出-
{ "_id" : ObjectId("5e47b1181627c0c63e7dba9b"), "Name" : "Chris" }
{ "_id" : ObjectId("5e47b11c1627c0c63e7dba9c"), "Name" : "Bob" }
{ "_id" : ObjectId("5e47b11f1627c0c63e7dba9d"), "Name" : "David" }以下是调用convertToCapped的查询-
> db.runCommand( { convertToCapped: 'demo260', size: 8345 } );
{ "ok" : 1 }这是要检查的查询stats()：
> db.demo260.stats()
这将产生以下输出-
{
"ns" : "test.demo260",
"size" : 112,
"count" : 3,
"avgObjSize" : 37,
"storageSize" : 16384,
"capped" : true,
"max" : -1,
"maxSize" : 8448,
"sleepCount" : 0,
"sleepMS" : 0,
"wiredTiger" : {
"metadata" : {
"formatVersion" : 1
},
"creationString" : "access_pattern_hint=none,allocation_size=4KB,app_metadata=(formatVersion=1),assert=(commit_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-61--7930664661263858819",
"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" : 3,
"blocks allocated" : 3,
"blocks freed" : 0,
"checkpoint size" : 4096,
"file allocation unit size" : 4096,
"file bytes available for reuse" : 0,
"file magic number" : 120897,
"file major version number" : 1,
"file size in bytes" : 16384,
"minor version number" : 0
},
"btree" : {
"btree checkpoint generation" : 0,
"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" : 0,
"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" : 514,
"bytes dirty in the cache cumulative" : 0,
"bytes read into cache" : 212,
"bytes written from cache" : 212,
"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" : 0,
"in-memory page splits" : 0,
"internal pages evicted" : 0,
"internal pages split during eviction" : 0,
"leaf pages split during eviction" : 0,
"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" : 2,
"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" : 4,
"pages seen by eviction walk" : 0,
"pages written from cache" : 2,
"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 pages read" : 0,
"compressed pages written" : 0,
"page written failed to compress" : 0,
"page written was too small to compress" : 2,
"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,
"close calls that result in cache" : 0,
"create calls" : 2,
"cursor operation restarted" : 0,
"cursor-insert key and value bytes inserted" : 115,
"cursor-remove key bytes removed" : 0,
"cursor-update value bytes updated" : 0,
"cursors reused from cache" : 0,
"insert calls" : 3,
"modify calls" : 0,
"next calls" : 0,
"prev calls" : 2,
"remove calls" : 0,
"reserve calls" : 0,
"reset calls" : 7,
"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" : 0,
"internal page multi-block writes" : 0,
"internal-page overflow keys" : 0,
"leaf page key bytes discarded using prefix compression" : 0,
"leaf page multi-block writes" : 0,
"leaf-page overflow keys" : 0,
"maximum blocks required for a page" : 0,
"overflow values written" : 0,
"page checksum matches" : 0,
"page reconciliation calls" : 2,
"page reconciliation calls for eviction" : 2,
"pages deleted" : 0
},
"session" : {
"cached cursor count" : 1,
"object compaction" : 0,
"open cursor count" : 0
},
"transaction" : {
"update conflicts" : 0
}
},
"nindexes" : 1,
"totalIndexSize" : 16384,
"indexSizes" : {
"_id_" : 16384
},
"ok" : 1
}