Create an Index

db.collection.createIndex( { name: -1 } )

Indexes — MongoDB Manual https://docs.mongodb.com/manual/indexes/

The following example creates a single key descending index on the name field:

db.collection.createIndex( { name: -1 } )

The db.collection.createIndex method only creates an index if an index of the same specification does not already exist.

添加索引前

repl_test:PRIMARY> db.ask.stats()
{
        "ns" : "test.ask",
        "ok" : 0,
        "errmsg" : "Collection [test.ask] not found."
}
repl_test:PRIMARY> use superdb
switched to db superdb
repl_test:PRIMARY> db.ask.stats()
{
        "ns" : "superdb.ask",
        "ok" : 0,
        "errmsg" : "Database [superdb] not found."
}
repl_test:PRIMARY> use superpub
switched to db superpub
repl_test:PRIMARY> db.ask.stats()
{
        "ns" : "superpub.ask",
        "size" : 55947749764,
        "count" : 124365523,
        "avgObjSize" : 449,
        "storageSize" : 40530432000,
        "capped" : false,
        "wiredTiger" : {
                "metadata" : {
                        "formatVersion" : 1
                },
                "creationString" : "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:superpub/collection-43--7896506117540609160",
                "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" : 2067891,
                        "blocks allocated" : 450483752,
                        "blocks freed" : 447893857,
                        "checkpoint size" : 40303841280,
                        "file allocation unit size" : 4096,
                        "file bytes available for reuse" : 226144256,
                        "file magic number" : 120897,
                        "file major version number" : 1,
                        "file size in bytes" : 40530432000,
                        "minor version number" : 0
                },
                "btree" : {
                        "btree checkpoint generation" : 420967,
                        "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" : 5,
                        "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" : 4991378563,
                        "bytes read into cache" : NumberLong("11308646402066"),
                        "bytes written from cache" : NumberLong("7591690744135"),
                        "checkpoint blocked page eviction" : 1879,
                        "data source pages selected for eviction unable to be evicted" : 174636635,
                        "hazard pointer blocked page eviction" : 185183,
                        "in-memory page passed criteria to be split" : 5479,
                        "in-memory page splits" : 2819,
                        "internal pages evicted" : 97777107,
                        "internal pages split during eviction" : 103,
                        "leaf pages split during eviction" : 85977,
                        "modified pages evicted" : 291652798,
                        "overflow pages read into cache" : 0,
                        "overflow values cached in memory" : 0,
                        "page split during eviction deepened the tree" : 2,
                        "page written requiring lookaside records" : 0,
                        "pages read into cache" : 489122504,
                        "pages read into cache requiring lookaside entries" : 0,
                        "pages requested from the cache" : 6291235571,
                        "pages written from cache" : 450117295,
                        "pages written requiring in-memory restoration" : 35361,
                        "unmodified pages evicted" : 208177468
                },
                "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" : 391290489,
                        "compressed pages written" : 252797204,
                        "page written failed to compress" : 22645,
                        "page written was too small to compress" : 197293964,
                        "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" : 41206,
                        "cursor-insert key and value bytes inserted" : 294104370212,
                        "cursor-remove key bytes removed" : 0,
                        "cursor-update value bytes updated" : 0,
                        "insert calls" : 555827217,
                        "next calls" : 1049991570,
                        "prev calls" : 2,
                        "remove calls" : 0,
                        "reset calls" : 2875034908,
                        "restarted searches" : 13727,
                        "search calls" : 1948368272,
                        "search near calls" : 8329976,
                        "truncate calls" : 0,
                        "update calls" : 0
                },
                "reconciliation" : {
                        "dictionary matches" : 0,
                        "fast-path pages deleted" : 0,
                        "internal page key bytes discarded using suffix compression" : 29084289,
                        "internal page multi-block writes" : 203924,
                        "internal-page overflow keys" : 0,
                        "leaf page key bytes discarded using prefix compression" : 0,
                        "leaf page multi-block writes" : 187019,
                        "leaf-page overflow keys" : 0,
                        "maximum blocks required for a page" : 19,
                        "overflow values written" : 0,
                        "page checksum matches" : 5052559,
                        "page reconciliation calls" : 446700880,
                        "page reconciliation calls for eviction" : 11010578,
                        "pages deleted" : 37
                },
                "session" : {
                        "object compaction" : 0,
                        "open cursor count" : 264
                },
                "transaction" : {
                        "update conflicts" : 1160210
                }
        },
        "nindexes" : 2,
        "totalIndexSize" : 4309454848,
        "indexSizes" : {
                "_id_" : 1232769024,
                "md5_1" : 3076685824
        },
        "ok" : 1
}

　　

添加索引

db.ask.createIndex( { keyword: -1 } )

Background Construction

Index Build Operations on a Populated Collection — MongoDB Manual https://docs.mongodb.com/manual/core/index-creation/#index-creation-background

 索引创建耗时，后台创建；

For potentially long running index building operations on standalone deployments, consider the backgroundoption so that the MongoDB  database remains available during the index building operation.

For example, to create an index in the background of the zipcode field of the people collection, issue the following:

db.people.createIndex( { zipcode: 1 }, { background: true } )