explain()

    类别

    SdbQuery

    描述

    获取查询的访问计划。

    options 参数详细说明如下：

    普通的访问计划

    Detail 选项为 false 时，将会展示普通的访问计划。

    垂直分区中主表的访问计划信息：

    垂直分区中子表的访问计划信息：

    详细的访问计划

    Detail 选项为 true 时，将会展示详细的访问计划。在协调节点和数据节点上展示的详细访问计划略有不同。

    Search 选项为 true 时，将会展示查询优化器搜索过的访问计划，并查看查询优化器选择的结果。

    请参考：。

    返回值

    返回访问计划的游标，类型为 object 。

    错误

    如果出错则抛异常，并输出错误信息，可以通过getLastErrMsg()获取错误信息或通过获取错误码。关于错误处理可以参考常见错误处理指南。

    • 普通表的访问计划
    • 垂直分区的访问计划
    1. {
    2.   "NodeName": "hostname:11830",
    3.   "GroupName": "group",
    4.   "Role": "data",
    5.   "Name": "maincs.maincl",
    6.   "SubCollections": [
    7.     {
    8.       "Name": "subcs.subcl1",
    9.       "ScanType": "tbscan",
    10.       "IndexName": "",
    11.       "UseExtSort": false,
    12.       "Query": {
    13.         "$and": []
    14.       },
    15.       "IXBound": null,
    16.       "NeedMatch": false,
    17.       "ReturnNum": 0,
    18.       "ElapsedTime": 0.000088,
    19.       "IndexRead": 0,
    20.       "DataRead": 0,
    21.       "UserCPU": 0,
    22.       "SysCPU": 0
    23.     },
    24.     {
    25.       "Name": "subcs.subcl2",
    26.       "ScanType": "tbscan",
    27.       "IndexName": "",
    28.       "UseExtSort": false,
    29.       "Query": {
    30.         "$and": []
    31.       },
    32.       "IXBound": null,
    33.       "NeedMatch": false,
    34.       "ReturnNum": 0,
    35.       "ElapsedTime": 0.000089,
    36.       "IndexRead": 0,
    37.       "DataRead": 0,
    38.       "UserCPU": 0,
    39.       "SysCPU": 0
    40.     }
    41.   ]
    42. }
    • 协调节点上的虚拟访问计划，即匹配符不能命中任何分区
    1. {
    2.   "NodeName": "hostname:11810",
    3.   "GroupName": "SYSCoord",
    4.   "Role": "coord",
    5.   "Collection": "maincs.maincl",
    6.   "Query": {
    7.     "a": 10000000
    8.   },
    9. }
    • 查看查询的普通访问计划，并使用 Run 选项执行查询
    • 使用 Detail 选项查看查询的详细访问计划
    1. > db.foo.bar.find( { a : { $gt : 100 } } ).explain( { Detail : true } )
    2. {
    3.   "NodeName": "hostname:11800",
    4.   "GroupName": "SYSCoord",
    5.   "Role": "coord",
    6.   "Collection": "foo.bar",
    7.   "Query": {
    8.     "a": {
    9.       "$gt": 100
    10.     }
    11.   },
    12.   "Sort": {},
    13.   "Selector": {},
    14.   "Hint": {},
    15.   "Skip": 0,
    16.   "Return": -1,
    17.   "Flag": 0,
    18.   "ReturnNum": 0,
    19.   "ElapsedTime": 0.00123,
    20.   "IndexRead": 0,
    21.   "DataRead": 0,
    22.   "UserCPU": 0,
    23.   "SysCPU": 0,
    24.   "PlanPath": {
    25.     "Operator": "COORD-MERGE",
    26.     "Sort": {},
    27.     "NeedReorder": false,
    28.     "DataNodeNum": 2,
    29.     "DataNodeList": [
    30.       {
    31.         "Name": "hostname:11810",
    32.         "EstTotalCost": 1.484
    33.       },
    34.       {
    35.         "Name": "hostname:11820",
    36.         "EstTotalCost": 0.7418349999999999
    37.       }
    38.     ],
    39.     "Selector": {},
    40.     "Skip": 0,
    41.     "Return": -1,
    42.     "Estimate": {
    43.       "StartCost": 0,
    44.       "RunCost": 1.5214865,
    45.       "TotalCost": 1.5214865,
    46.       "Output": {
    47.         "Records": 74973,
    48.         "RecordSize": 29,
    49.         "Sorted": false
    50.       }
    51.     },
    52.     "ChildOperators": [
    53.       {
    54.         "NodeName": "hostname:11810",
    55.         "GroupName": "group1",
    56.         "Role": "data",
    57.         "Collection": "foo.bar",
    58.         "Query": {
    59.           "a": {
    60.             "$gt": 100
    61.           }
    62.         },
    63.         "Sort": {},
    64.         "Selector": {},
    65.         "Hint": {},
    66.         "Skip": 0,
    67.         "Return": -1,
    68.         "Flag": 2048,
    69.         "ReturnNum": 0,
    70.         "ElapsedTime": 0.000078,
    71.         "IndexRead": 0,
    72.         "DataRead": 0,
    73.         "UserCPU": 0,
    74.         "SysCPU": 0,
    75.         "CacheStatus": "HitCache",
    76.         "MainCLPlan": false,
    77.         "CacheLevel": "OPT_PLAN_PARAMETERIZED",
    78.         "Parameters": [
    79.           100
    80.         ],
    81.         "MatchConfig": {
    82.           "EnableMixCmp": false,
    83.           "Parameterized": true,
    84.           "FuzzyOptr": false
    85.         }
    86.       },
    87.       {
    88.         "NodeName": "hostname:11820",
    89.         "GroupName": "group2",
    90.         "Role": "data",
    91.         "Collection": "foo.bar",
    92.         "Query": {
    93.           "a": {
    94.             "$gt": 100
    95.           }
    96.         },
    97.         "Sort": {},
    98.         "Selector": {},
    99.         "Hint": {},
    100.         "Skip": 0,
    101.         "Return": -1,
    102.         "Flag": 2048,
    103.         "ReturnNum": 0,
    104.         "ElapsedTime": 0.000081,
    105.         "IndexRead": 0,
    106.         "DataRead": 0,
    107.         "UserCPU": 0,
    108.         "SysCPU": 0,
    109.         "CacheStatus": "HitCache",
    110.         "MainCLPlan": false,
    111.         "CacheLevel": "OPT_PLAN_PARAMETERIZED",
    112.         "Parameters": [
    113.           100
    114.         ],
    115.         "MatchConfig": {
    116.           "EnableMixCmp": false,
    117.           "Parameterized": true,
    118.           "FuzzyOptr": false
    119.         }
    120.       }
    121.     ]
    122.   }
    123. }
    • 使用 Detail 选项查看查询的详细访问计划，并使用 Run 选项执行查询
    1. > db.foo.bar.find( { a : { $gt : 100 } } ).explain( { Detail : true, Run : true } )
    2. {
    3.   "NodeName": "hostname:11800",
    4.   "GroupName": "SYSCoord",
    5.   "Role": "coord",
    6.   "Collection": "foo.bar",
    7.   "Query": {
    8.     "a": {
    9.       "$gt": 100
    10.     }
    11.   },
    12.   "Sort": {},
    13.   "Selector": {},
    14.   "Hint": {},
    15.   "Skip": 0,
    16.   "Return": -1,
    17.   "Flag": 0,
    18.   "ReturnNum": 99899,
    19.   "ElapsedTime": 0.82863,
    20.   "IndexRead": 0,
    21.   "DataRead": 0,
    22.   "UserCPU": 0.01999999999999999,
    23.   "SysCPU": 0.009999999999999995,
    24.   "PlanPath": {
    25.     "Operator": "COORD-MERGE",
    26.     "Sort": {},
    27.     "NeedReorder": false,
    28.     "DataNodeNum": 2,
    29.     "DataNodeList": [
    30.       {
    31.         "Name": "hostname:11820",
    32.         "EstTotalCost": 0.7418349999999999,
    33.         "QueryTimeSpent": 0.733299,
    34.         "WaitTimeSpent": 0.013556
    35.       },
    36.       {
    37.         "Name": "hostname:11810",
    38.         "EstTotalCost": 1.484,
    39.         "QueryTimeSpent": 0.82677,
    40.         "WaitTimeSpent": 0.084652
    41.       }
    42.     ],
    43.     "Selector": {},
    44.     "Skip": 0,
    45.     "Return": -1,
    46.     "Estimate": {
    47.       "StartCost": 0,
    48.       "RunCost": 1.5214865,
    49.       "TotalCost": 1.5214865,
    50.       "Output": {
    51.         "Records": 74973,
    52.         "RecordSize": 29,
    53.         "Sorted": false
    54.       }
    55.     },
    56.     "Run": {
    57.       "ContextID": 29314,
    58.       "StartTimestamp": "2017-12-14-15.24.51.254623",
    59.       "QueryTimeSpent": 0.821182,
    60.       "GetMores": 112,
    61.       "ReturnNum": 99899,
    62.       "WaitTimeSpent": 0.075
    63.     },
    64.     "ChildOperators": [
    65.       {
    66.         "NodeName": "hostname:11820",
    67.         "GroupName": "group2",
    68.         "Role": "data",
    69.         "Collection": "foo.bar",
    70.         "Query": {
    71.           "a": {
    72.             "$gt": 100
    73.           }
    74.         },
    75.         "Sort": {},
    76.         "Selector": {},
    77.         "Hint": {},
    78.         "Skip": 0,
    79.         "Return": -1,
    80.         "Flag": 2048,
    81.         "ReturnNum": 49892,
    82.         "ElapsedTime": 0.733493,
    83.         "IndexRead": 0,
    84.         "DataRead": 49945,
    85.         "UserCPU": 0.14,
    86.         "SysCPU": 0.01000000000000001,
    87.         "CacheStatus": "HitCache",
    88.         "MainCLPlan": false,
    89.         "CacheLevel": "OPT_PLAN_PARAMETERIZED",
    90.           100
    91.         ],
    92.         "MatchConfig": {
    93.           "EnableMixCmp": false,
    94.           "Parameterized": true,
    95.           "FuzzyOptr": false
    96.         }
    97.       },
    98.       {
    99.         "NodeName": "hostname:11810",
    100.         "GroupName": "group1",
    101.         "Role": "data",
    102.         "Collection": "foo.bar",
    103.         "Query": {
    104.           "a": {
    105.             "$gt": 100
    106.           }
    107.         },
    108.         "Sort": {},
    109.         "Selector": {},
    110.         "Hint": {},
    111.         "Skip": 0,
    112.         "Return": -1,
    113.         "Flag": 2048,
    114.         "ReturnNum": 50007,
    115.         "ElapsedTime": 0.82666,
    116.         "IndexRead": 0,
    117.         "DataRead": 50055,
    118.         "UserCPU": 0.1499999999999986,
    119.         "SysCPU": 0.01000000000000023,
    120.         "CacheStatus": "HitCache",
    121.         "MainCLPlan": false,
    122.         "CacheLevel": "OPT_PLAN_PARAMETERIZED",
    123.         "Parameters": [
    124.           100
    125.         ],
    126.         "MatchConfig": {
    127.           "EnableMixCmp": false,
    128.           "Parameterized": true,
    129.           "FuzzyOptr": false
    130.         }
    131.       }
    132.     ]
    133.   }
    134. }
    • 使用 Detail 选项查看查询的详细访问计划，并且使用 Search 选项查看查询优化器的搜索过程
    • 使用 Detail 选项查看查询的详细访问计划，并且使用 Location 选项查看查询在 group1 上的访问计划
    1. > db.foo.bar.find( { a : { $gt : 100 } } ).explain( { Detail : true, Location : { GroupName : 'group1' } } )
    2. {
    3.   "NodeName": "hostname:11800",
    4.   "GroupName": "SYSCoord",
    5.   "Role": "coord",
    6.   "Collection": "foo.bar",
    7.   "Query": {
    8.     "a": {
    9.       "$gt": 100
    10.     }
    11.   },
    12.   "Sort": {},
    13.   "Selector": {},
    14.   "Hint": {},
    15.   "Skip": 0,
    16.   "Return": -1,
    17.   "Flag": 0,
    18.   "ReturnNum": 0,
    19.   "ElapsedTime": 0.011374,
    20.   "IndexRead": 0,
    21.   "DataRead": 0,
    22.   "UserCPU": 0,
    23.   "SysCPU": 0,
    24.   "PlanPath": {
    25.     "Operator": "COORD-MERGE",
    26.     "Sort": {},
    27.     "NeedReorder": false,
    28.     "DataNodeNum": 2,
    29.     "DataNodeList": [
    30.       {
    31.         "Name": "hostname:11810",
    32.         "EstTotalCost": 1.484
    33.       },
    34.       {
    35.         "Name": "hostname:11820",
    36.         "EstTotalCost": 0.7418349999999999
    37.       }
    38.     ],
    39.     "Selector": {},
    40.     "Skip": 0,
    41.     "Return": -1,
    42.     "Estimate": {
    43.       "StartCost": 0,
    44.       "RunCost": 1.5214865,
    45.       "TotalCost": 1.5214865,
    46.       "Output": {
    47.         "Records": 74973,
    48.         "RecordSize": 29,
    49.         "Sorted": false
    50.       }
    51.     },
    52.     "ChildOperators": [
    53.       {
    54.         "NodeName": "hostname:11810",
    55.         "GroupName": "group1",
    56.         "Role": "data",
    57.         "Collection": "foo.bar",
    58.         "Query": {
    59.           "a": {
    60.             "$gt": 100
    61.           }
    62.         },
    63.         "Sort": {},
    64.         "Selector": {},
    65.         "Hint": {},
    66.         "Skip": 0,
    67.         "Return": -1,
    68.         "Flag": 2048,
    69.         "ReturnNum": 0,
    70.         "ElapsedTime": 0.000088,
    71.         "IndexRead": 0,
    72.         "DataRead": 0,
    73.         "UserCPU": 0,
    74.         "SysCPU": 0,
    75.         "CacheStatus": "HitCache",
    76.         "MainCLPlan": false,
    77.         "CacheLevel": "OPT_PLAN_PARAMETERIZED",
    78.         "Parameters": [
    79.           100
    80.         ],
    81.         "MatchConfig": {
    82.           "EnableMixCmp": false,
    83.           "Parameterized": true,
    84.           "FuzzyOptr": false
    85.         }
    86.       }
    87.     ]
    88.   }
    89. }
    • 使用 Detail 选项查看垂直分区的详细访问计划，并使用 Expand 选项展开所有细节
    1. > db.maincs.maincl.find( { a : { $gt : 100 } } ).explain( { Detail : true, Expand : true } )
    2. {
    3.   "NodeName": "hostname:11800",
    4.   "GroupName": "SYSCoord",
    5.   "Role": "coord",
    6.   "Collection": "maincs.maincl",
    7.   "Query": {
    8.     "a": {
    9.       "$gt": 100
    10.     }
    11.   },
    12.   "Sort": {},
    13.   "Selector": {},
    14.   "Hint": {},
    15.   "Skip": 0,
    16.   "Return": -1,
    17.   "Flag": 0,
    18.   "ReturnNum": 0,
    19.   "ElapsedTime": 0.002748,
    20.   "IndexRead": 0,
    21.   "DataRead": 0,
    22.   "UserCPU": 0,
    23.   "SysCPU": 0,
    24.   "PlanPath": {
    25.     "Operator": "COORD-MERGE",
    26.     "Sort": {},
    27.     "NeedReorder": false,
    28.     "DataNodeNum": 2,
    29.     "DataNodeList": [
    30.       {
    31.         "Name": "hostname:11810",
    32.         "EstTotalCost": 0.9624999999999999
    33.       },
    34.       {
    35.         "Name": "hostname:11820",
    36.         "EstTotalCost": 0.9624999999999999
    37.       }
    38.     ],
    39.     "Selector": {},
    40.     "Skip": 0,
    41.     "Return": -1,
    42.     "Estimate": {
    43.       "StartCost": 0,
    44.       "RunCost": 0.9874999999999999,
    45.       "TotalCost": 0.9874999999999999,
    46.       "Output": {
    47.         "Records": 50000,
    48.         "RecordSize": 43,
    49.         "Sorted": false
    50.       }
    51.     },
    52.     "ChildOperators": [
    53.       {
    54.         "NodeName": "hostname:11810",
    55.         "GroupName": "group1",
    56.         "Role": "data",
    57.         "Collection": "maincs.maincl",
    58.         "Query": {
    59.           "a": {
    60.             "$gt": 100
    61.           }
    62.         },
    63.         "Sort": {},
    64.         "Selector": {},
    65.         "Hint": {},
    66.         "Skip": 0,
    67.         "Return": -1,
    68.         "Flag": 2048,
    69.         "ReturnNum": 0,
    70.         "ElapsedTime": 0.00062,
    71.         "IndexRead": 0,
    72.         "DataRead": 0,
    73.         "UserCPU": 0,
    74.         "SysCPU": 0,
    75.         "PlanPath": {
    76.           "Operator": "MERGE",
    77.           "Sort": {},
    78.           "NeedReorder": false,
    79.           "SubCollectionNum": 2,
    80.           "SubCollectionList": [
    81.             {
    82.               "Name": "subcs.subcl2",
    83.               "EstTotalCost": 0.475
    84.             },
    85.             {
    86.               "Name": "subcs.subcl1",
    87.               "EstTotalCost": 0.475
    88.             }
    89.           ],
    90.           "Selector": {},
    91.           "Skip": 0,
    92.           "Return": -1,
    93.           "Estimate": {
    94.             "StartCost": 0,
    95.             "RunCost": 0.9624999999999999,
    96.             "TotalCost": 0.9624999999999999,
    97.             "Output": {
    98.               "Records": 25000,
    99.               "RecordSize": 43,
    100.               "Sorted": false
    101.             }
    102.           },
    103.           "SubCollections": [
    104.             {
    105.               "Collection": "subcs.subcl2",
    106.               "Query": {
    107.                 "a": {
    108.                   "$gt": 100
    109.                 }
    110.               },
    111.               "Sort": {},
    112.               "Selector": {},
    113.               "Hint": {},
    114.               "Skip": 0,
    115.               "Return": -1,
    116.               "Flag": 2048,
    117.               "ReturnNum": 0,
    118.               "ElapsedTime": 0.000042,
    119.               "IndexRead": 0,
    120.               "DataRead": 0,
    121.               "UserCPU": 0,
    122.               "SysCPU": 0,
    123.               "CacheStatus": "HitCache",
    124.               "MainCLPlan": true,
    125.               "CacheLevel": "OPT_PLAN_PARAMETERIZED",
    126.               "Parameters": [
    127.                 100
    128.               ],
    129.               "MatchConfig": {
    130.                 "EnableMixCmp": false,
    131.                 "Parameterized": true,
    132.                 "FuzzyOptr": false
    133.               },
    134.               "PlanPath": {
    135.                 "Operator": "TBSCAN",
    136.                 "Collection": "subcs.subcl2",
    137.                 "Query": {
    138.                   "$and": [
    139.                     {
    140.                       "a": {
    141.                         "$gt": 100
    142.                       }
    143.                     }
    144.                   ]
    145.                 "Selector": {},
    146.                 "Skip": 0,
    147.                 "Return": -1,
    148.                 "Estimate": {
    149.                   "StartCost": 0,
    150.                   "RunCost": 0.475,
    151.                   "TotalCost": 0.475,
    152.                   "CLEstFromStat": false,
    153.                   "Input": {
    154.                     "Pages": 25,
    155.                     "Records": 25000,
    156.                     "RecordSize": 43
    157.                   },
    158.                   "Filter": {
    159.                     "MthSelectivity": 0.4999994999999995
    160.                   },
    161.                   "Output": {
    162.                     "Records": 12500,
    163.                     "RecordSize": 43,
    164.                     "Sorted": false
    165.                   }
    166.                 }
    167.               }
    168.             },
    169.             {
    170.               "Collection": "subcs.subcl1",
    171.               "Query": {
    172.                 "a": {
    173.                   "$gt": 100
    174.                 }
    175.               },
    176.               "Sort": {},
    177.               "Selector": {},
    178.               "Hint": {},
    179.               "Skip": 0,
    180.               "Return": -1,
    181.               "Flag": 2048,
    182.               "ReturnNum": 0,
    183.               "ElapsedTime": 0.000049,
    184.               "IndexRead": 0,
    185.               "DataRead": 0,
    186.               "UserCPU": 0,
    187.               "SysCPU": 0,
    188.               "CacheStatus": "HitCache",
    189.               "MainCLPlan": true,
    190.               "CacheLevel": "OPT_PLAN_PARAMETERIZED",
    191.               "Parameters": [
    192.                 100
    193.               ],
    194.               "MatchConfig": {
    195.                 "EnableMixCmp": false,
    196.                 "Parameterized": true,
    197.                 "FuzzyOptr": false
    198.               },
    199.               "PlanPath": {
    200.                 "Operator": "TBSCAN",
    201.                 "Collection": "subcs.subcl1",
    202.                 "Query": {
    203.                   "$and": [
    204.                     {
    205.                       "a": {
    206.                         "$gt": 100
    207.                       }
    208.                     }
    209.                   ]
    210.                 },
    211.                 "Selector": {},
    212.                 "Skip": 0,
    213.                 "Return": -1,
    214.                 "Estimate": {
    215.                   "StartCost": 0,
    216.                   "RunCost": 0.475,
    217.                   "TotalCost": 0.475,
    218.                   "CLEstFromStat": false,
    219.                   "Input": {
    220.                     "Pages": 25,
    221.                     "Records": 25000,
    222.                     "RecordSize": 43
    223.                   },
    224.                   "Filter": {
    225.                     "MthSelectivity": 0.4999994999999995
    226.                   },
    227.                   "Output": {
    228.                     "Records": 12500,
    229.                     "RecordSize": 43,
    230.                     "Sorted": false
    231.                   }
    232.                 }
    233.               }
    234.             }
    235.           ]
    236.         }
    237.       },
    238.       {
    239.         "NodeName": "hostname:11820",
    240.         "GroupName": "group2",
    241.         "Role": "data",
    242.         "Collection": "maincs.maincl",
    243.         "Query": {
    244.           "a": {
    245.             "$gt": 100
    246.           }
    247.         },
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