$regex prefix search with escaped "|" should use tighter index bounds

Initialization > db.version() 3.0.6 > db.test_search.drop() true > for ( var i=1;i<=100;i++){db.test_search.save({_id: "id" +i})} WriteResult({ "nMatched" : 0, "nUpserted" : 1, "nModified" : 0, "_id" : "id100" }) > db.test_search.find().limit(3) { "_id" : "id1" } { "_id" : "id2" } { "_id" : "id3" } > db.test_search.find().count() 100 search and view mongodb log(run with verbose) 1. search with | > db.test_search.find({_id:/^id\|/}) > db.test_search.find({_id:/^id\|sssssssss/}) > db.test_search.find({_id:{ "$regex" : "^id\\|" }}) > db.test_search.find({_id:{ "$regex" : "^id\\|sssssssss" }}) mongodb v3.0.6 log show that "nscanned:100" 2015-09-16T15:10:21.551+0800 I QUERY [conn2128] query test.test_search query: { _id: /^id\|/ } planSummary: IXSCAN { _id: 1 } ntoreturn:0 ntoskip:0 nscanned:100 nscannedObjects:0 keyUpdates:0 writeConflicts:0 numYields:0 nreturned:0 reslen:20 locks:{ Global: { acquireCount: { r: 2 } }, MMAPV1Journal: { acquireCount: { r: 1 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { R: 1 } } } 0ms   2015-09-16T15:10:55.456+0800 I QUERY [conn2128] query test.test_search query: { _id: /^id\|sssssssss/ } planSummary: IXSCAN { _id: 1 } ntoreturn:0 ntoskip:0 nscanned:100 nscannedObjects:0 keyUpdates:0 writeConflicts:0 numYields:0 nreturned:0 reslen:20 locks:{ Global: { acquireCount: { r: 2 } }, MMAPV1Journal: { acquireCount: { r: 1 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { R: 1 } } } 0ms   2015-09-16T15:11:16.113+0800 I QUERY [conn2128] query test.test_search query: { _id: { $regex: "^id\|" } } planSummary: IXSCAN { _id: 1 } ntoreturn:0 ntoskip:0 nscanned:100 nscannedObjects:0 keyUpdates:0 writeConflicts:0 numYields:0 nreturned:0 reslen:20 locks:{ Global: { acquireCount: { r: 2 } }, MMAPV1Journal: { acquireCount: { r: 1 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { R: 1 } } } 0ms   2015-09-16T15:11:34.034+0800 I QUERY [conn2128] query test.test_search query: { _id: { $regex: "^id\|sssssssss" } } planSummary: IXSCAN { _id: 1 } ntoreturn:0 ntoskip:0 nscanned:100 nscannedObjects:0 keyUpdates:0 writeConflicts:0 numYields:0 nreturned:0 reslen:20 locks:{ Global: { acquireCount: { r: 2 } }, MMAPV1Journal: { acquireCount: { r: 1 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { R: 1 } } } 0ms we also tested in v2.4.7, same query showed "nscanned:0" Wed Sep 16 15:43:40.854 [conn3077] query test.test_search query: { _id: /^id\|/ } ntoreturn:0 ntoskip:0 nscanned:0 keyUpdates:0 locks(micros) r:3882 nreturned:0 reslen:20 3ms   Wed Sep 16 15:43:57.683 [conn3077] query test.test_search query: { _id: /^id\|sssssssss/ } ntoreturn:0 ntoskip:0 nscanned:0 keyUpdates:0 locks(micros) r:115 nreturned:0 reslen:20 0ms   Wed Sep 16 15:44:06.890 [conn3077] query test.test_search query: { _id: { $regex: "^id\|" } } ntoreturn:0 ntoskip:0 nscanned:0 keyUpdates:0 locks(micros) r:168 nreturned:0 reslen:20 0ms   Wed Sep 16 15:44:13.571 [conn3077] query test.test_search query: { _id: { $regex: "^id\|sssssssss" } } ntoreturn:0 ntoskip:0 nscanned:0 keyUpdates:0 locks(micros) r:121 nreturned:0 reslen:20 0ms 2. search without | > db.test_search.find({_id:/^idA/}) > db.test_search.find({_id:/^id\?/}) mongodb v3.0.6 show that "nscanned:0", this is expected 2015-09-16T15:16:25.091+0800 I QUERY [conn2128] query test.test_search query: { _id: /^idA/ } planSummary: IXSCAN { _id: 1 } ntoreturn:0 ntoskip:0 nscanned:0 nscannedObjects:0 keyUpdates:0 writeConflicts:0 numYields:0 nreturned:0 reslen:20 locks:{ Global: { acquireCount: { r: 2 } }, MMAPV1Journal: { acquireCount: { r: 1 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { R: 1 } } } 1ms   2015-09-16T15:16:51.971+0800 I QUERY [conn2128] query test.test_search query: { _id: /^id\?/ } planSummary: IXSCAN { _id: 1 } ntoreturn:0 ntoskip:0 nscanned:0 nscannedObjects:0 keyUpdates:0 writeConflicts:0 numYields:0 nreturned:0 reslen:20 locks:{ Global: { acquireCount: { r: 2 } }, MMAPV1Journal: { acquireCount: { r: 1 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { R: 1 } } } 0ms mongodb explain info > db.test_search.find({_id:/^id\|/}).explain() { "queryPlanner" : { "plannerVersion" : 1, "namespace" : "test.test_search", "indexFilterSet" : false, "parsedQuery" : { "_id" : /^id\|/ }, "winningPlan" : { "stage" : "FETCH", "inputStage" : { "stage" : "IXSCAN", "filter" : { "_id" : /^id\|/ }, "keyPattern" : { "_id" : 1 }, "indexName" : "_id_", "isMultiKey" : false, "direction" : "forward", "indexBounds" : { "_id" : [ "[\"\", {})", "[/^id\\|/, /^id\\|/]" ] } } }, "rejectedPlans" : [ ] }, "serverInfo" : { "host" : "test.local", "port" : 27017, "version" : "3.0.6", "gitVersion" : "nogitversion" }, "ok" : 1 } >   > db.test_search.find({_id:/^idA/}).explain() { "queryPlanner" : { "plannerVersion" : 1, "namespace" : "test.test_search", "indexFilterSet" : false, "parsedQuery" : { "_id" : /^idA/ }, "winningPlan" : { "stage" : "FETCH", "inputStage" : { "stage" : "IXSCAN", "keyPattern" : { "_id" : 1 }, "indexName" : "_id_", "isMultiKey" : false, "direction" : "forward", "indexBounds" : { "_id" : [ "[\"idA\", \"idB\")", "[/^idA/, /^idA/]" ] } } }, "rejectedPlans" : [ ] }, "serverInfo" : { "host" : "test.local", "port" : 27017, "version" : "3.0.6", "gitVersion" : "nogitversion" }, "ok" : 1 } >