mongodb compound index over extending -

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i have question regarding compound indexes cant seem find, or maybe have misunderstood.

lets have created compound index {a:1, b:1, c:1}. should make according http://docs.mongodb.org/manual/core/indexes/#compound-indexes

the following queries fast.

db.test.find({a:"a", b:"b",c:"c"}) db.test.find({a:"a", b:"b"}) db.test.find({a:"a"})

as understand order of query important, explicit subset of {a:"a", b:"b",c:"c"} order important?

lets query

db.test.find({d:"d",e:"e",a:"a", b:"b",c:"c"})

or

db.test.find({a:"a", b:"b",c:"c",d:"d",e:"e"})

will these render useless specific compound index?

compound indexes in mongodb work on prefix mechanism whereby a , {a,b} considered prefixes, order, of compound index, however, order of fields in query not matter.

so lets take examples:

db.test.find({d:"d",e:"e",a:"a", b:"b",c:"c"})

will use index:

db.ghghg.find({d:1,e:1,a:1,c:1,b:1}).explain() {         "cursor" : "btreecursor a_1_b_1_c_1",         "ismultikey" : false,         "n" : 1,         "nscannedobjects" : 1,         "nscanned" : 1,         "nscannedobjectsallplans" : 2,         "nscannedallplans" : 2,         "scanandorder" : false,         "indexonly" : false,         "nyields" : 0,         "nchunkskips" : 0,         "millis" : 0,         "indexbounds" : {                 "a" : [                         [                                 1,                                 1                         ]                 ],                 "b" : [                         [                                 1,                                 1                         ]                 ],                 "c" : [                         [                                 1,                                 1                         ]                 ]         },         "server" : "ubuntu:27017" }

since a , b there.

db.test.find({a:"a", b:"b",c:"c",d:"d",e:"e"})

depends upon selectivity , cardinality of d , e. use compound index whether use in such manner allows decent performance of query depends heavily upon what's in there.


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