mongodb 持久化(3)

1. 载体崩溃 当出现硬件问题或文件系统出错，特别是硬盘损坏了，就没法保护数据安全了。另外，不同品牌的硬件和软件具有不同的持久保证的。总而言之，如果硬件或文件系统破坏了数据，MongoDB是无法保护数据的，这已经属于底层存储的事情了。可以使用复制来避

1. 载体崩溃

当出现硬件问题或文件系统出错，特别是硬盘损坏了，就没法保护数据安全了。另外，不同品牌的硬件和软件具有不同的持久保证的。总而言之，如果硬件或文件系统破坏了数据，MongoDB是无法保护数据的，这已经属于底层存储的事情了。可以使用复制来避免这个问题，其实就是单点问题了。

2. ?检查损坏

validate命令用来检测一个集合的损坏，如：

> db.posts.validate({full:true}){        "ns" : "ttlsa_com.posts",        "firstExtent" : "1:1036000 ns:ttlsa_com.posts",        "lastExtent" : "4:2000 ns:ttlsa_com.posts",        "extentCount" : 14,        "extents" : [                {                        "loc" : "1:1036000",                        "xnext" : "1:104e000",                        "xprev" : "null",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 61440,                        "firstRecord" : "1:1037c30",                        "lastRecord" : "1:103e4f0"                },                {                        "loc" : "1:104e000",                        "xnext" : "1:108a000",                        "xprev" : "1:1036000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 245760,                        "firstRecord" : "1:104e0b0",                        "lastRecord" : "1:10556b0"                },                {                        "loc" : "1:108a000",                        "xnext" : "1:117a000",                        "xprev" : "1:104e000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 983040,                        "firstRecord" : "1:108a0b0",                        "lastRecord" : "1:109a9b0"                },                {                        "loc" : "1:117a000",                        "xnext" : "1:155e000",                        "xprev" : "1:108a000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 3932160,                        "firstRecord" : "1:117a0b0",                        "lastRecord" : "1:13739f0"                },                {                        "loc" : "1:155e000",                        "xnext" : "1:24ee000",                        "xprev" : "1:117a000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 15728640,                        "firstRecord" : "1:155e0b0",                        "lastRecord" : "1:1bbe4f0"                },                {                        "loc" : "1:24ee000",                        "xnext" : "1:392e000",                        "xprev" : "1:155e000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 21233664,                        "firstRecord" : "1:24ee8b0",                        "lastRecord" : "1:2b485b0"                },                {                        "loc" : "1:392e000",                        "xnext" : "1:56c5000",                        "xprev" : "1:24ee000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 28667904,                        "firstRecord" : "1:392e0b0",                        "lastRecord" : "1:450dd30"                },                {                        "loc" : "1:56c5000",                        "xnext" : "2:2000",                        "xprev" : "1:392e00<b style="color:transparent">本文来源gao@!dai!ma.com搞$$代^@码网*</b>0",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 38703104,                        "firstRecord" : "1:56c50b0",                        "lastRecord" : "1:617c0b0"                },                {                        "loc" : "2:2000",                        "xnext" : "2:3ad7000",                        "xprev" : "1:56c5000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 52252672,                        "firstRecord" : "2:20b0",                        "lastRecord" : "2:188ac30"                },                {                        "loc" : "2:3ad7000",                        "xnext" : "2:7e1d000",                        "xprev" : "2:2000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 70541312,                        "firstRecord" : "2:3ad7470",                        "lastRecord" : "2:66b8af0"                },                {                        "loc" : "2:7e1d000",                        "xnext" : "3:2000",                        "xprev" : "2:3ad7000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 95232000,                        "firstRecord" : "2:7e1d0b0",                        "lastRecord" : "2:be8a2b0"                },                {                        "loc" : "3:2000",                        "xnext" : "3:dd21000",                        "xprev" : "2:7e1d000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 128565248,                        "firstRecord" : "3:20b0",                        "lastRecord" : "3:63eb670"                },                {                        "loc" : "3:dd21000",                        "xnext" : "4:2000",                        "xprev" : "3:2000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 173563904,                        "firstRecord" : "3:dd210b0",                        "lastRecord" : "3:12fccc30"                },                {                        "loc" : "4:2000",                        "xnext" : "null",                        "xprev" : "3:dd21000",                        "nsdiag" : "ttlsa_com.posts",                        "size" : 234311680,                        "firstRecord" : "4:20b0",                        "lastRecord" : "4:7bec3b0"                }        ],        "datasize" : 614217440,        "nrecords" : 305603,        "lastExtentSize" : 234311680,        "padding" : 1.0000000000221079,        "firstExtentDetails" : {                "loc" : "1:1036000",                "xnext" : "1:104e000",                "xprev" : "null",                "nsdiag" : "ttlsa_com.posts",                "size" : 61440,                "firstRecord" : "1:1037c30",                "lastRecord" : "1:103e4f0"        },        "lastExtentDetails" : {                "loc" : "4:2000",                "xnext" : "null",                "xprev" : "3:dd21000",                "nsdiag" : "ttlsa_com.posts",                "size" : 234311680,                "firstRecord" : "4:20b0",                "lastRecord" : "4:7bec3b0"        },        "objectsFound" : 305603,        "invalidObjects" : 0,        "bytesWithHeaders" : 619107088,        "bytesWithoutHeaders" : 614217440,        "deletedCount" : 125358,        "deletedSize" : 244912976,        "nIndexes" : 9,        "keysPerIndex" : {                "ttlsa_com.posts.$_id_" : 305603,                "ttlsa_com.posts.$index_doctorSn" : 305603,                "ttlsa_com.posts.$index_doctorUid" : 305603,                "ttlsa_com.posts.$index_hosDeptId" : 305603,                "ttlsa_com.posts.$index_hospitalId" : 305603,                "ttlsa_com.posts.$doctorNumberList_1_doctorOrderId_-1" : 305924,                "ttlsa_com.posts.$cityId_1_displayStatus_1" : 305603,                "ttlsa_com.posts.$standardDeptId_1_displayStatus_1" : 305603,                "ttlsa_com.posts.$doctorCode_1" : 305603        },        "valid" : true,        "errors" : [ ],        "ok" : 1}

在上面输出底部，有个”valid” : true 说明没有损坏，如果不是，会找到一些损坏的细节。大部分输出是描述集合内部的结构，对于调试不是特别有用的。只能检测集合，不能检测索引。如果出现无效的BSONbj，通常就是损坏了。最糟糕的是出现pdfile，pdfile基本上是mongodb的数据存储核心，几乎可以判断数据文件已经损坏了。如果出现损坏，会看到下面的日志信息：Tue Dec 20 01:12:09 [initandlisten] Assertion: 10334:Invalid BSONObj size: 285213831 (0x87040011)first element: _id: ObjectId(‘4e5efa454b4ae20fa6000013’)如果第一个元素显示的是垃圾，不需要做什么。如果第一个元素是可见的，可以移除损坏的文档。如：> db.remove({_id: ObjectId(‘4e5efa454b4ae20fa6000013’)})如果损坏并不局限于该文档，这种技术可能无法工作，你仍然需要进行修复。

3. 复制的持久性

复制集一个写可被回滚，直到它被写入到一个大多数的集合中。> db.runCommand({“getLastError” : 1, “j” : true, “w” : “majority”})只能保证primary写入已经持久化，secondary未必持久化。

原文地址：mongodb 持久化(3), 感谢原作者分享。

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