Mongodb 中全文索引居然比正则慢

版本：

> version() 3.4.3 

创建全文索引：

> db.tests.createIndex({'a':'text'}) # a 字段的值很大超过 1024 个字符 

查询

> db.tests.find({'$text':{'$search':'ere'}).explain('executionStats') "executionStats" : { "executionSuccess" : true, "nReturned" : 80018, "executionTimeMillis" : 306877, "totalKeysExamined" : 83546, "totalDocsExamined" : 83546, "executionStages" : { "stage" : "TEXT", "nReturned" : 80018, "executionTimeMillisEstimate" : 306699, "works" : 167095, "advanced" : 80018, "needTime" : 87076, "needYield" : 0, "saveState" : 16525, "restoreState" : 16525, "isEOF" : 1, "invalidates" : 0, "indexPrefix" : { }, "indexName" : "a_text", "parsedTextQuery" : { "terms" : [ "ii" ], "negatedTerms" : [ ], "phrases" : [ "ere" ], "negatedPhrases" : [ ] }, "textIndexVersion" : 3, "inputStage" : { "stage" : "TEXT_MATCH", "nReturned" : 80018, "executionTimeMillisEstimate" : 306649, "works" : 167095, "advanced" : 80018, "needTime" : 87076, "needYield" : 0, "saveState" : 16525, "restoreState" : 16525, "isEOF" : 1, "invalidates" : 0, "docsRejected" : 3528, "inputStage" : { "stage" : "TEXT_OR", "nReturned" : 83546, "executionTimeMillisEstimate" : 305932, "works" : 167095, "advanced" : 83546, "needTime" : 83548, "needYield" : 0, "saveState" : 16525, "restoreState" : 16525, "isEOF" : 1, "invalidates" : 0, "docsExamined" : 83546, "inputStage" : { "stage" : "IXSCAN", "nReturned" : 83546, "executionTimeMillisEstimate" : 1103, "works" : 83547, "advanced" : 83546, "needTime" : 0, "needYield" : 0, "saveState" : 16525, "restoreState" : 16525, "isEOF" : 1, "invalidates" : 0, "keyPattern" : { "_fts" : "text", "_ftsx" : 1 }, "indexName" : "a_text", "isMultiKey" : true, "isUnique" : false, "isSparse" : false, "isPartial" : false, "indexVersion" : 2, "direction" : "backward", "indexBounds" : { }, "keysExamined" : 83546, "seeks" : 1, "dupsTested" : 83546, "dupsDropped" : 0, "seenInvalidated" : 0 } 

1，不是很理解，为什么需要做 TEXT_OR 和 TEXT_MATCH 的操作？

理想状态下，全文索引应该比正则快，要不然还要全文索引干什么，但是，如上的查询条件使用正则（无论存不存在 b_text 索引，和避免热数据，重启 mongo ）都是一样的结果

> db.tests.find({'a':{'$regex':'ere','$options':'i'}}).explain('executionStats') "executionStats" : { "executionSuccess" : true, "nReturned" : 81319, "executionTimeMillis" : 101701, "totalKeysExamined" : 0, "totalDocsExamined" : 4256954123, "executionStages" : { "stage" : "COLLSCAN", "filter" : { "a" : { "$regex" : "ere", "$options" : "i" } }, "nReturned" : 81319, "executionTimeMillisEstimate" : 101391, "works" : 4256956, "advanced" : 81319, "needTime" : 4175636, "needYield" : 0, "saveState" : 33964, "restoreState" : 33964, "isEOF" : 1, "invalidates" : 0, "direction" : "forward", "docsExamined" : 4256954 } 

是不是我打开的方式不对呢？麻烦给指点一下。谢谢