mongoDB-Explain

新版的MongoDB中的Explain已经变样了

Explain支持三种Mode

queryPlanner Mode

db.collection.explain()　　默认mode是queryPlanner，返回queryPlanner信息

executionStats Mode

当前mode返回queryPlanner和executionStats信息

allPlansExecution Mode

更加详细的信息~

比如：我这里有10万数据，做一个查询

db.my_collection.stats()
{
    "ns" : "test.my_collection",
    "size" : ,
    "count" : 100500,
    "avgObjSize" : ,
    "storageSize" : ,
    "capped" : false,
    "wiredTiger" : {
        "metadata" : {
            "formatVersion" :
        },
        "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_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-8--701343360468677485",
        "LSM" : {
            "bloom filter false positives" : ,
            "bloom filter hits" : ,
            "bloom filter misses" : ,
            "bloom filter pages evicted from cache" : ,
            "bloom filter pages read into cache" : ,
            "bloom filters in the LSM tree" : ,
            "chunks in the LSM tree" : ,
            "highest merge generation in the LSM tree" : ,
            "queries that could have benefited from a Bloom filter that did not exist" : ,
            "sleep for LSM checkpoint throttle" : ,
            "sleep for LSM merge throttle" : ,
            "total size of bloom filters" :
        },
        "block-manager" : {
            "allocations requiring file extension" : ,
            "blocks allocated" : ,
            "blocks freed" : ,
            "checkpoint size" : ,
            "file allocation unit size" : ,
            "file bytes available for reuse" : ,
            "file magic number" : ,
            "file major version number" : ,
            "file size in bytes" : ,
            "minor version number" :
        },
        "btree" : {
            "btree checkpoint generation" : ,
            "column-store fixed-size leaf pages" : ,
            "column-store internal pages" : ,
            "column-store variable-size RLE encoded values" : ,
            "column-store variable-size deleted values" : ,
            "column-store variable-size leaf pages" : ,
            "fixed-record size" : ,
            "maximum internal page key size" : ,
            "maximum internal page size" : ,
            "maximum leaf page key size" : ,
            "maximum leaf page size" : ,
            "maximum leaf page value size" : ,
            "maximum tree depth" : ,
            "number of key/value pairs" : ,
            "overflow pages" : ,
            "pages rewritten by compaction" : ,
            "row-store internal pages" : ,
            "row-store leaf pages" :
        },
        "cache" : {
            "bytes currently in the cache" : ,
            "bytes read into cache" : ,
            "bytes written from cache" : ,
            "checkpoint blocked page eviction" : ,
            "data source pages selected for eviction unable to be evicted" : ,
            "eviction walk passes of a file" : ,
            "eviction walk target pages histogram - 0-9" : ,
            "eviction walk target pages histogram - 10-31" : ,
            "eviction walk target pages histogram - 128 and higher" : ,
            "eviction walk target pages histogram - 32-63" : ,
            "eviction walk target pages histogram - 64-128" : ,
            "eviction walks abandoned" : ,
            "eviction walks gave up because they restarted their walk twice" : ,
            "eviction walks gave up because they saw too many pages and found no candidates" : ,
            "eviction walks gave up because they saw too many pages and found too few candidates" : ,
            "eviction walks reached end of tree" : ,
            "eviction walks started from root of tree" : ,
            "eviction walks started from saved location in tree" : ,
            "hazard pointer blocked page eviction" : ,
            "in-memory page passed criteria to be split" : ,
            "in-memory page splits" : ,
            "internal pages evicted" : ,
            "internal pages split during eviction" : ,
            "leaf pages split during eviction" : ,
            "modified pages evicted" : ,
            "overflow pages read into cache" : ,
            "page split during eviction deepened the tree" : ,
            "page written requiring lookaside records" : ,
            "pages read into cache" : ,
            "pages read into cache after truncate" : ,
            "pages read into cache after truncate in prepare state" : ,
            "pages read into cache requiring lookaside entries" : ,
            "pages requested from the cache" : ,
            "pages seen by eviction walk" : ,
            "pages written from cache" : ,
            "pages written requiring in-memory restoration" : ,
            "tracked dirty bytes in the cache" : ,
            "unmodified pages evicted" :
        },
        "cache_walk" : {
            "Average difference between current eviction generation when the page was last considered" : ,
            "Average on-disk page image size seen" : ,
            "Average time in cache for pages that have been visited by the eviction server" : ,
            "Average time in cache for pages that have not been visited by the eviction server" : ,
            "Clean pages currently in cache" : ,
            "Current eviction generation" : ,
            "Dirty pages currently in cache" : ,
            "Entries in the root page" : ,
            "Internal pages currently in cache" : ,
            "Leaf pages currently in cache" : ,
            "Maximum difference between current eviction generation when the page was last considered" : ,
            "Maximum page size seen" : ,
            "Minimum on-disk page image size seen" : ,
            "Number of pages never visited by eviction server" : ,
            "On-disk page image sizes smaller than a single allocation unit" : ,
            "Pages created in memory and never written" : ,
            "Pages currently queued for eviction" : ,
            "Pages that could not be queued for eviction" : ,
            "Refs skipped during cache traversal" : ,
            "Size of the root page" : ,
            "Total number of pages currently in cache" :
        },
        "compression" : {
            "compressed pages read" : ,
            "compressed pages written" : ,
            "page written failed to compress" : ,
            "page written was too small to compress" : ,
            "raw compression call failed, additional data available" : ,
            "raw compression call failed, no additional data available" : ,
            "raw compression call succeeded" :
        },
        "cursor" : {
            "bulk-loaded cursor-insert calls" : ,
            "create calls" : ,
            "cursor-insert key and value bytes inserted" : ,
            "cursor-remove key bytes removed" : ,
            "cursor-update value bytes updated" : ,
            "cursors cached on close" : ,
            "cursors reused from cache" : ,
            "insert calls" : ,
            "modify calls" : ,
            "next calls" : ,
            "prev calls" : ,
            "remove calls" : ,
            "reserve calls" : ,
            "reset calls" : ,
            "restarted searches" : ,
            "search calls" : ,
            "search near calls" : ,
            "truncate calls" : ,
            "update calls" :
        },
        "reconciliation" : {
            "dictionary matches" : ,
            "fast-path pages deleted" : ,
            "internal page key bytes discarded using suffix compression" : ,
            "internal page multi-block writes" : ,
            "internal-page overflow keys" : ,
            "leaf page key bytes discarded using prefix compression" : ,
            "leaf page multi-block writes" : ,
            "leaf-page overflow keys" : ,
            "maximum blocks required for a page" : ,
            "overflow values written" : ,
            "page checksum matches" : ,
            "page reconciliation calls" : ,
            "page reconciliation calls for eviction" : ,
            "pages deleted" :
        },
        "session" : {
            "cached cursor count" : ,
            "object compaction" : ,
            "open cursor count" :
        },
        "transaction" : {
            "update conflicts" :
        }
    },
    "nindexes" : ,
    "totalIndexSize" : ,
    "indexSizes" : {
        "_id_" :
    },
    "ok" :
}

以上是查看表信息的。。

下面查询id为25000的数据，我们以executionStats Mode 来查看

db.my_collection.find({_id:{$eq:}})
{ "_id" : NumberLong(), "name" : "Book-25000", "_class" : "com.example.demo.entity.Book" }
db.my_collection.explain("executionStats").find({_id:{$eq:}})
{
    "queryPlanner" : {
        "plannerVersion" : ,
        "namespace" : "test.my_collection",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "_id" : {
                "$eq" :
            }
        },
        "winningPlan" : {
            "stage" : "FETCH",
            "inputStage" : {
                "stage" : "IXSCAN",
                "keyPattern" : {
                    "_id" :
                },
                "indexName" : "_id_",
                "isMultiKey" : false,
                "multiKeyPaths" : {
                    "_id" : [ ]
                },
                "isUnique" : true,
                "isSparse" : false,
                "isPartial" : false,
                "indexVersion" : ,
                "direction" : "forward",
                "indexBounds" : {
                    "_id" : [
                        "[25000.0, 25000.0]"
                    ]
                }
            }
        },
        "rejectedPlans" : [ ]
    },
    "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : ,
        "executionTimeMillis" : ,
        "totalKeysExamined" : ,
        "totalDocsExamined" : ,
        "executionStages" : {
            "stage" : "FETCH",
            "nReturned" : ,
            "executionTimeMillisEstimate" : ,
            "works" : ,
            "advanced" : ,
            "needTime" : ,
            "needYield" : ,
            "saveState" : ,
            "restoreState" : ,
            "isEOF" : ,
            "invalidates" : ,
            "docsExamined" : ,
            "alreadyHasObj" : ,
            "inputStage" : {
                "stage" : "IXSCAN",
                "nReturned" : ,
                "executionTimeMillisEstimate" : ,
                "works" : ,
                "advanced" : ,
                "needTime" : ,
                "needYield" : ,
                "saveState" : ,
                "restoreState" : ,
                "isEOF" : ,
                "invalidates" : ,
                "keyPattern" : {
                    "_id" :
                },
                "indexName" : "_id_",
                "isMultiKey" : false,
                "multiKeyPaths" : {
                    "_id" : [ ]
                },
                "isUnique" : true,
                "isSparse" : false,
                "isPartial" : false,
                "indexVersion" : ,
                "direction" : "forward",
                "indexBounds" : {
                    "_id" : [
                        "[25000.0, 25000.0]"
                    ]
                },
                "keysExamined" : ,
                "seeks" : ,
                "dupsTested" : ,
                "dupsDropped" : ,
                "seenInvalidated" :
            }
        }
    },
    "serverInfo" : {
        "host" : "——",
        "port" : ,
        "version" : "3.6.5",
        "gitVersion" : "a20ecd3e3a174162052ff99913bc2ca9a839d618"
    },
    "ok" :
}

下面解释一下关心的参数：

explain.executionStats.nReturned    　　　　 查询匹配的文档数

explain.executionStats.executionTimeMillis    查询所需要的时间（单位为毫秒）

explain.executionStats.totalKeysExamined    扫描的索引数

explain.executionStats.totalDocsExamined    扫描的文档数

explain.executionStats.allPlansExecution    只有以allPlansExecution模式运行才会显示这个字段

上面查询，用到了索引，匹配的文档数为1，时间为0（因为没有费力），索引数为1，扫描的文档数为1

那么下面我计划一个笨查询

db.my_collection.explain("executionStats").find()
{
    "queryPlanner" : {
        "plannerVersion" : ,
        "namespace" : "test.my_collection",
        "indexFilterSet" : false,
        "parsedQuery" : {

        },
        "winningPlan" : {
            "stage" : "COLLSCAN",
            "direction" : "forward"
        },
        "rejectedPlans" : [ ]
    },
    "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : ,
        "executionTimeMillis" : ,
        "totalKeysExamined" : ,
        "totalDocsExamined" : ,
        "executionStages" : {
            "stage" : "COLLSCAN",
            "nReturned" : ,
            "executionTimeMillisEstimate" : ,
            "works" : ,
            "advanced" : ,
            "needTime" : ,
            "needYield" : ,
            "saveState" : ,
            "restoreState" : ,
            "isEOF" : ,
            "invalidates" : ,
            "direction" : "forward",
            "docsExamined" :
        }
    },
    "serverInfo" : {
        "host" : "FC001977PC1",
        "port" : ,
        "version" : "3.6.5",
        "gitVersion" : "a20ecd3e3a174162052ff99913bc2ca9a839d618"
    },
    "ok" :
}

这样数据就明显一点了，不过话说回来，查这么多数据只用了39毫秒，的确挺牛逼的

更具体的说明见官网：https://docs.mongodb.com/manual/reference/method/db.collection.explain/#db.collection.explain

PS：无意间在官网上发现在线练习的控制台：https://docs.mongodb.com/manual/tutorial/insert-documents/