Jan*_*Tan 3 database mongodb nosql
最初我们的服务器从 4 个分片开始。在网站运行几年后，我们决定再添加 4 个分片来帮助减轻现有服务器的负载，现在的问题是分片分布非常不均匀，因此新服务器没有帮助减轻负载. 以下是我们较大的集合之一的分片分布示例
Shard shard0000 contains 15.56% data, 15.56% docs in cluster, avg obj size on shard : 143B
Shard shard0001 contains 15.12% data, 15.12% docs in cluster, avg obj size on shard : 143B
Shard shard0002 contains 16.73% data, 16.73% docs in cluster, avg obj size on shard : 143B
Shard shard0003 contains 15.62% data, 15.62% docs in cluster, avg obj size on shard : 143B
Shard shard0004 contains 9.31% data, 9.31% docs in cluster, avg obj size on shard : 143B
Shard shard0005 contains 9.35% data, 9.35% docs in cluster, avg obj size on shard : 143B
Shard shard0006 contains 9.12% data, 9.12% docs in cluster, avg obj size on shard : 143B
Shard shard0007 contains 9.16% data, 9.16% docs in cluster, avg obj size on shard : 143B
平衡器一直在非高峰时段运行，但似乎并没有解决分布不均的问题。
有什么建议？
更新：sh.status()为集合添加了
shard key: { "hash" : 1 }
chunks:
shard0004 21
shard0007 20
shard0006 20
shard0005 21
shard0002 24
shard0003 24
shard0001 24
shard0000 25
{ "hash" : { "$minKey" : 1 } } -->> { "hash" : "0096c316a754c8f628793402d6a217fa" } on : shard0004 Timestamp(28, 0)
{ "hash" : "0096c316a754c8f628793402d6a217fa" } -->> { "hash" : "01767732a77657e2e67e3b1d1afa6216" } on : shard0007 Timestamp(65, 0)
{ "hash" : "01767732a77657e2e67e3b1d1afa6216" } -->> { "hash" : "0256566c72f3d75dff16b5740bf60df3" } on : shard0004 Timestamp(66, 0)
{ "hash" : "0256566c72f3d75dff16b5740bf60df3" } -->> { "hash" : "0323ebd846f1897351bf904092492253" } on : shard0006 Timestamp(68, 0)
{ "hash" : "0323ebd846f1897351bf904092492253" } -->> { "hash" : "03f0faf2bc0b91570816c1811b1bf89e" } on : shard0007 Timestamp(69, 0)
{ "hash" : "03f0faf2bc0b91570816c1811b1bf89e" } -->> { "hash" : "04acc3c7bbfb66570601e88a498598ae" } on : shard0007 Timestamp(73, 0)
{ "hash" : "04acc3c7bbfb66570601e88a498598ae" } -->> { "hash" : "056891c4103e62d7f6d90afc6bc0113c" } on : shard0004 Timestamp(74, 0)
{ "hash" : "056891c4103e62d7f6d90afc6bc0113c" } -->> { "hash" : "06250a5a7c6d0985c1b0d975d005b216" } on : shard0005 Timestamp(75, 0)
{ "hash" : "06250a5a7c6d0985c1b0d975d005b216" } -->> { "hash" : "06e17baaaf9c74bb4a94e80b8c5be56b" } on : shard0006 Timestamp(76, 0)
{ "hash" : "06e17baaaf9c74bb4a94e80b8c5be56b" } -->> { "hash" : "079c56d507673f2a7a0f11aad27da3c7" } on : shard0005 Timestamp(79, 0)
{ "hash" : "079c56d507673f2a7a0f11aad27da3c7" } -->> { "hash" : "08585cf98b8f1d5027ead5622d770e32" } on : shard0006 Timestamp(80, 0)
{ "hash" : "08585cf98b8f1d5027ead5622d770e32" } -->> { "hash" : "091404f3a9faf42c75c1fe7ccd87c1ba" } on : shard0006 Timestamp(84, 0)
{ "hash" : "091404f3a9faf42c75c1fe7ccd87c1ba" } -->> { "hash" : "09cfc86384d3b0ff5c4ed3ee8ecfda3d" } on : shard0004 Timestamp(86, 0)
{ "hash" : "09cfc86384d3b0ff5c4ed3ee8ecfda3d" } -->> { "hash" : "0b0719d7022b9d6d831c4253dd9861ed" } on : shard0005 Timestamp(87, 0)
{ "hash" : "0b0719d7022b9d6d831c4253dd9861ed" } -->> { "hash" : "0f601a06372d8874b4ff4dc58b9ac0e6" } on : shard0002 Timestamp(87, 1)
{ "hash" : "0f601a06372d8874b4ff4dc58b9ac0e6" } -->> { "hash" : "10c7fb288ab4657d63c40df3cee5eec5" } on : shard0002 Timestamp(60, 16)
{ "hash" : "10c7fb288ab4657d63c40df3cee5eec5" } -->> { "hash" : "121a5790eea9e48113dbf13bc920381c" } on : shard0002 Timestamp(71, 4)
{ "hash" : "121a5790eea9e48113dbf13bc920381c" } -->> { "hash" : "1346f4d9e28529070ddd5d7ce630b824" } on : shard0002 Timestamp(86, 16)
{ "hash" : "1346f4d9e28529070ddd5d7ce630b824" } -->> { "hash" : "1692c5e0adbae6847c1595976cf308e8" } on : shard0002 Timestamp(86, 17)
{ "hash" : "1692c5e0adbae6847c1595976cf308e8" } -->> { "hash" : "1817e8910d67a14a1ccb0ce68074f283" } on : shard0004 Timestamp(24, 0)
{ "hash" : "1817e8910d67a14a1ccb0ce68074f283" } -->> { "hash" : "199d8813d2533204d363c0eb05508d5a" } on : shard0005 Timestamp(25, 0)
{ "hash" : "199d8813d2533204d363c0eb05508d5a" } -->> { "hash" : "1b23becfb6b654b7a830311a709c1eb8" } on : shard0006 Timestamp(26, 0)
{ "hash" : "1b23becfb6b654b7a830311a709c1eb8" } -->> { "hash" : "1caa0fe0fc3a76ce12de781137cbb2e0" } on : shard0007 Timestamp(27, 0)
{ "hash" : "1caa0fe0fc3a76ce12de781137cbb2e0" } -->> { "hash" : "1e83e11811d7dd326f15f1ff16fb8d7f" } on : shard0007 Timestamp(43, 0)
{ "hash" : "1e83e11811d7dd326f15f1ff16fb8d7f" } -->> { "hash" : "204473f57239f124b5e2fa6a0ce5b3de" } on : shard0004 Timestamp(45, 0)
{ "hash" : "204473f57239f124b5e2fa6a0ce5b3de" } -->> { "hash" : "2122bff14ade54acabf809fcdd9fb3fb" } on : shard0005 Timestamp(59, 0)
{ "hash" : "2122bff14ade54acabf809fcdd9fb3fb" } -->> { "hash" : "2201978401c65849099954200f0d98c6" } on : shard0007 Timestamp(61, 0)
{ "hash" : "2201978401c65849099954200f0d98c6" } -->> { "hash" : "2365f97f0af5b10ef082ac2fa94213c7" } on : shard0004 Timestamp(62, 0)
{ "hash" : "2365f97f0af5b10ef082ac2fa94213c7" } -->> { "hash" : "2423ecbcb32549275ea1bbead7f1a6d2" } on : shard0005 Timestamp(63, 0)
{ "hash" : "2423ecbcb32549275ea1bbead7f1a6d2" } -->> { "hash" : "24e204818b0e5dfa8c62c1840b7b36c9" } on : shard0006 Timestamp(64, 0)
{ "hash" : "24e204818b0e5dfa8c62c1840b7b36c9" } -->> { "hash" : "26a8fcef33cdb12ca0f9c8e964884e25" } on : shard0004 Timestamp(12, 0)
{ "hash" : "26a8fcef33cdb12ca0f9c8e964884e25" } -->> { "hash" : "286fdb86a0ad33fce45d48ba8aeaed76" } on : shard0005 Timestamp(13, 0)
{ "hash" : "286fdb86a0ad33fce45d48ba8aeaed76" } -->> { "hash" : "2a36d5c6818e42393dff73fd9d36825e" } on : shard0006 Timestamp(14, 0)
{ "hash" : "2a36d5c6818e42393dff73fd9d36825e" } -->> { "hash" : "2bfd3f123776c882402fb366caae69ef" } on : shard0007 Timestamp(15, 0)
{ "hash" : "2bfd3f123776c882402fb366caae69ef" } -->> { "hash" : "2dc863db22aa527a1ab5c38fb4c5b79f" } on : shard0004 Timestamp(16, 0)
{ "hash" : "2dc863db22aa527a1ab5c38fb4c5b79f" } -->> { "hash" : "2f952392172750d70ad3b33e52409dd7" } on : shard0005 Timestamp(17, 0)
{ "hash" : "2f952392172750d70ad3b33e52409dd7" } -->> { "hash" : "316103318efd305dba54b3de6aeaa4e8" } on : shard0006 Timestamp(18, 0)
{ "hash" : "316103318efd305dba54b3de6aeaa4e8" } -->> { "hash" : "332f1bacc24a66fd63d9a709a473d883" } on : shard0007 Timestamp(19, 0)
{ "hash" : "332f1bacc24a66fd63d9a709a473d883" } -->> { "hash" : "3494d9e02071844bcc3d452f9279589f" } on : shard0005 Timestamp(29, 0)
{ "hash" : "3494d9e02071844bcc3d452f9279589f" } -->> { "hash" : "35fb652c9a3222f995fe94f43cc771e0" } on : shard0006 Timestamp(30, 0)
{ "hash" : "35fb652c9a3222f995fe94f43cc771e0" } -->> { "hash" : "3762fd13a6ce6ad6660b760762db63de" } on : shard0007 Timestamp(31, 0)
{ "hash" : "3762fd13a6ce6ad6660b760762db63de" } -->> { "hash" : "38ca4719fbd5c7043d406a0c3212f50d" } on : shard0004 Timestamp(32, 0)
{ "hash" : "38ca4719fbd5c7043d406a0c3212f50d" } -->> { "hash" : "39ba62b8fc12ec9a82e814ae22abc639" } on : shard0007 Timestamp(57, 0)
{ "hash" : "39ba62b8fc12ec9a82e814ae22abc639" } -->> { "hash" : "3aab998023c585aee431faf50ccad1be" } on : shard0004 Timestamp(58, 0)
{ "hash" : "3aab998023c585aee431faf50ccad1be" } -->> { "hash" : "3c3b142b4600a277253d62a9e59495fb" } on : shard0006 Timestamp(60, 0)
{ "hash" : "3c3b142b4600a277253d62a9e59495fb" } -->> { "hash" : "3d91ce54fad93712c7cac10143618671" } on : shard0005 Timestamp(67, 0)
{ "hash" : "3d91ce54fad93712c7cac10143618671" } -->> { "hash" : "3e9e53ff48d9a9da3c783937f52ac178" } on : shard0004 Timestamp(70, 0)
{ "hash" : "3e9e53ff48d9a9da3c783937f52ac178" } -->> { "hash" : "3fab92c377ea67884e77eec02751b822" } on : shard0005 Timestamp(71, 0)
{ "hash" : "3fab92c377ea67884e77eec02751b822" } -->> { "hash" : "406b30881e6627f7cd5b4473e7b295b5" } on : shard0006 Timestamp(72, 0)
{ "hash" : "406b30881e6627f7cd5b4473e7b295b5" } -->> { "hash" : "412bbe8c021e45cd03389921abef23d8" } on : shard0007 Timestamp(77, 0)
{ "hash" : "412bbe8c021e45cd03389921abef23d8" } -->> { "hash" : "41d96299f6865b2dc1791a5e8d3870fa" } on : shard0004 Timestamp(82, 0)
{ "hash" : "41d96299f6865b2dc1791a5e8d3870fa" } -->> { "hash" : "4287d3ac80457ced47c2204a61c89c4e" } on : shard0005 Timestamp(83, 0)
{ "hash" : "4287d3ac80457ced47c2204a61c89c4e" } -->> { "hash" : "43c9eac00f88103926311705c65a592f" } on : shard0007 Timestamp(85, 0)
{ "hash" : "43c9eac00f88103926311705c65a592f" } -->> { "hash" : "448cc55c43dcc80a5b3ee365408294de" } on : shard0004 Timestamp(90, 0)
{ "hash" : "448cc55c43dcc80a5b3ee365408294de" } -->> { "hash" : "454fd98710d7f6b8a6ca42c116a720be" } on : shard0005 Timestamp(91, 0)
{ "hash" : "454fd98710d7f6b8a6ca42c116a720be" } -->> { "hash" : "4613a1f5e7623aa2b8ce5220ef207428" } on : shard0006 Timestamp(92, 0)
{ "hash" : "4613a1f5e7623aa2b8ce5220ef207428" } -->> { "hash" : "46d6b1749a62824ec317fda78d436ec4" } on : shard0007 Timestamp(93, 0)
{ "hash" : "46d6b1749a62824ec317fda78d436ec4" } -->> { "hash" : "479ad065a429d297cae7234419eb1d9d" } on : shard0004 Timestamp(94, 0)
{ "hash" : "479ad065a429d297cae7234419eb1d9d" } -->> { "hash" : "485e5b8cf9f8f5a8245f7b893ac60240" } on : shard0005 Timestamp(95, 0)
{ "hash" : "485e5b8cf9f8f5a8245f7b893ac60240" } -->> { "hash" : "49b2ee2792b86873e7891f43453478b6" } on : shard0003 Timestamp(95, 1)
{ "hash" : "49b2ee2792b86873e7891f43453478b6" } -->> { "hash" : "4aee88c9976990eb2f2e52a6ea6b4d0b" } on : shard0003 Timestamp(81, 14)
{ "hash" : "4aee88c9976990eb2f2e52a6ea6b4d0b" } -->> { "hash" : "4c042e5b974325dd87e8c2093cb7809f" } on : shard0003 Timestamp(91, 4)
{ "hash" : "4c042e5b974325dd87e8c2093cb7809f" } -->> { "hash" : "4f01c23152e8c23eb685f0f1ccd3574a" } on : shard0003 Timestamp(91, 5)
{ "hash" : "4f01c23152e8c23eb685f0f1ccd3574a" } -->> { "hash" : "507cddde3ffb51492a3a32457b3c8680" } on : shard0003 Timestamp(60, 4)
{ "hash" : "507cddde3ffb51492a3a32457b3c8680" } -->> { "hash" : "51d74c15a9832c5ab881354835e7c3f0" } on : shard0003 Timestamp(66, 10)
{ "hash" : "51d74c15a9832c5ab881354835e7c3f0" } -->> { "hash" : "5327cd130720e69b56164d5bc7cf47e2" } on : shard0003 Timestamp(76, 4)
{ "hash" : "5327cd130720e69b56164d5bc7cf47e2" } -->> { "hash" : "54426cbf461bb1a3a43f44012f8afaf8" } on : shard0003 Timestamp(89, 4)
{ "hash" : "54426cbf461bb1a3a43f44012f8afaf8" } -->> { "hash" : "558078d76f9ba43477bacbed2640414b" } on : shard0003 Timestamp(89, 5)
{ "hash" : "558078d76f9ba43477bacbed2640414b" } -->> { "hash" : "56fac1c343349227bc39c5f72be82dd4" } on : shard0003 Timestamp(56, 14)
{ "hash" : "56fac1c343349227bc39c5f72be82dd4" } -->> { "hash" : "5854da68fae12e4afdb32ec5172698cc" } on : shard0003 Timestamp(66, 12)
{ "hash" : "5854da68fae12e4afdb32ec5172698cc" } -->> { "hash" : "59a4d26a918d536e8da3eb3c48b8b66e" } on : shard0003 Timestamp(71, 8)
{ "hash" : "59a4d26a918d536e8da3eb3c48b8b66e" } -->> { "hash" : "5c134f1e081b25e0be638c97ac45f9fe" } on : shard0003 Timestamp(71, 9)
{ "hash" : "5c134f1e081b25e0be638c97ac45f9fe" } -->> { "hash" : "5dd232bd88633d2a6d8b81a26d6a4bf6" } on : shard0003 Timestamp(39, 18)
{ "hash" : "5dd232bd88633d2a6d8b81a26d6a4bf6" } -->> { "hash" : "5f69838082adb58883e5e4b6ac36ebe7" } on : shard0003 Timestamp(49, 16)
{ "hash" : "5f69838082adb58883e5e4b6ac36ebe7" } -->> { "hash" : "60b31719bcb9d2e9da906c8ef24d6b58" } on : shard0003 Timestamp(81, 4)
{ "hash" : "60b31719bcb9d2e9da906c8ef24d6b58" } -->> { "hash" : "61d843a4a9fb8c3ded6806732d8d7c32" } on : shard0003 Timestamp(87, 6)
{ "hash" : "61d843a4a9fb8c3ded6806732d8d7c32" } -->> { "hash" : "6480d1d4442a1d46d750f68744c53d94" } on : shard0003 Timestamp(87, 7)
{ "hash" : "6480d1d4442a1d46d750f68744c53d94" } -->> { "hash" : "663e424de9bd7f712ea89caf50d73cf5" } on : shard0003 Timestamp(39, 16)
{ "hash" : "663e424de9bd7f712ea89caf50d73cf5" } -->> { "hash" : "67edb97c800788a891fb500deb400256" } on : shard0003 Timestamp(49, 6)
{ "hash" : "67edb97c800788a891fb500deb400256" } -->> { "hash" : "697083691bee96e22eb50bdbefb8917b" } on : shard0003 Timestamp(56, 6)
{ "hash" : "697083691bee96e22eb50bdbefb8917b" } -->> { "hash" : "6ae3c71cdff25b79d4102c2863d422fb" } on : shard0003 Timestamp(60, 12)
{ "hash" : "6ae3c71cdff25b79d4102c2863d422fb" } -->> { "hash" : "6c33fe587906a9f7bf6bcab78c6c1608" } on : shard0003 Timestamp(76, 14)
{ "hash" : "6c33fe587906a9f7bf6bcab78c6c1608" } -->> { "hash" : "6ed3040f678900d16c948ba19fe786bc" } on : shard0003 Timestamp(76, 15)
{ "hash" : "6ed3040f678900d16c948ba19fe786bc" } -->> { "hash" : "702c035c360f5278d683f77606c69ebb" } on : shard0002 Timestamp(66, 8)
{ "hash" : "702c035c360f5278d683f77606c69ebb" } -->> { "hash" : "71760e9813a6229d9116801328db471d" } on : shard0002 Timestamp(78, 6)
{ "hash" : "71760e9813a6229d9116801328db471d" } -->> { "hash" : "74973d49c7393320989bd87d212e74e0" } on : shard0002 Timestamp(78, 7)
{ "hash" : "74973d49c7393320989bd87d212e74e0" } -->> { "hash" : "761336135e0d2046bb5924e32c989d0f" } on : shard0002 Timestamp(56, 12)
{ "hash" : "761336135e0d2046bb5924e32c989d0f" } -->> { "hash" : "7789da25534f6a446163857b6ca80585" } on : shard0002 Timestamp(60, 6)
{ "hash" : "7789da25534f6a446163857b6ca80585" } -->> { "hash" : "78dba031c7d4f5130a7138a990d03777" } on : shard0002 Timestamp(71, 6)
{ "hash" : "78dba031c7d4f5130a7138a990d03777" } -->> { "hash" : "7b9d5cd8befd19bb11b26a2063e99a79" } on : shard0002 Timestamp(71, 7)
{ "hash" : "7b9d5cd8befd19bb11b26a2063e99a79" } -->> { "hash" : "7d22b7f188a06e82a2d539257e134141" } on : shard0002 Timestamp(56, 4)
{ "hash" : "7d22b7f188a06e82a2d539257e134141" } -->> { "hash" : "7e8afb407f89298187a18109d0c0f9e6" } on : shard0002 Timestamp(60, 18)
{ "hash" : "7e8afb407f89298187a18109d0c0f9e6" } -->> { "hash" : "7fef03cc84df8c33ec72904140b9a5fe" } on : shard0002 Timestamp(60, 24)
{ "hash" : "7fef03cc84df8c33ec72904140b9a5fe" } -->> { "hash" : "81380bbdd0d4d07c5dd600250f0444af" } on : shard0002 Timestamp(81, 8)
{ "hash" : "81380bbdd0d4d07c5dd600250f0444af" } -->> { "hash" : "82e680a43d730066c6d6d00f1be4e32a" } on : shard0002 Timestamp(81, 9)
{ "hash" : "82e680a43d730066c6d6d00f1be4e32a" } -->> { "hash" : "846f27eef8b26bc874a030920d6f2dc8" } on : shard0002 Timestamp(53, 8)
{ "hash" : "846f27eef8b26bc874a030920d6f2dc8" } -->> { "hash" : "85e2740d4d83be8292c24412db7a00a1" } on : shard0002 Timestamp(60, 10)
{ "hash" : "85e2740d4d83be8292c24412db7a00a1" } -->> { "hash" : "873ed6e94dbe4d4b798cf819a7be9f87" } on : shard0002 Timestamp(66, 6)
{ "hash" : "873ed6e94dbe4d4b798cf819a7be9f87" } -->> { "hash" : "886dab713c8c5fe42494dc487232b405" } on : shard0002 Timestamp(86, 14)
{ "hash" : "886dab713c8c5fe42494dc487232b405" } -->> { "hash" : "8b453172ecbdb48e5877e6cfc7b79ee3" } on : shard0002 Timestamp(86, 15)
{ "hash" : "8b453172ecbdb48e5877e6cfc7b79ee3" } -->> { "hash" : "8c148b1f1f6976ac486993ef2701e934" } on : shard0004 Timestamp(78, 0)
{ "hash" : "8c148b1f1f6976ac486993ef2701e934" } -->> { "hash" : "8ce30d15961ce62b15e60eaf814ce45e" } on : shard0007 Timestamp(81, 0)
{ "hash" : "8ce30d15961ce62b15e60eaf814ce45e" } -->> { "hash" : "8d9918897a24d6a64456b784f490b048" } on : shard0006 Timestamp(88, 0)
{ "hash" : "8d9918897a24d6a64456b784f490b048" } -->> { "hash" : "8e4fabc8ca097b36debc0896b8b9a974" } on : shard0007 Timestamp(89, 0)
{ "hash" : "8e4fabc8ca097b36debc0896b8b9a974" } -->> { "hash" : "8fb407f11e1212c4240ec06a979615b0" } on : shard0001 Timestamp(89, 1)
{ "hash" : "8fb407f11e1212c4240ec06a979615b0" } -->> { "hash" : "90fdd7ab184255c02b99edda101796ae" } on : shard0001 Timestamp(78, 8)
{ "hash" : "90fdd7ab184255c02b99edda101796ae" } -->> { "hash" : "94337e2ed8741d02028c33f5a238f2cd" } on : shard0001 Timestamp(78, 9)
{ "hash" : "94337e2ed8741d02028c33f5a238f2cd" } -->> { "hash" : "95f40c00417a5a8ee692d459570a8551" } on : shard0001 Timestamp(39, 8)
{ "hash" : "95f40c00417a5a8ee692d459570a8551" } -->> { "hash" : "97a4a2771fbf4e2633dae4d3009cb8b1" } on : shard0001 Timestamp(49, 4)
{ "hash" : "97a4a2771fbf4e2633dae4d3009cb8b1" } -->> { "hash" : "99407767d9a265c1b19e506500b44aa5" } on : shard0001 Timestamp(49, 10)
{ "hash" : "99407767d9a265c1b19e506500b44aa5" } -->> { "hash" : "9acc0d7e5308c0cb60d959db94d33318" } on : shard0001 Timestamp(53, 4)
{ "hash" : "9acc0d7e5308c0cb60d959db94d33318" } -->> { "hash" : "9c419a178e32a05c2650cd31efcc858d" } on : shard0001 Timestamp(60, 8)
{ "hash" : "9c419a178e32a05c2650cd31efcc858d" } -->> { "hash" : "9d8f77175b877cfc8febdf733e0a3f7a" } on : shard0001 Timestamp(76, 16)
{ "hash" : "9d8f77175b877cfc8febdf733e0a3f7a" } -->> { "hash" : "9fbacbf5c378be80449aefcc198bfc68" } on : shard0001 Timestamp(76, 17)
{ "hash" : "9fbacbf5c378be80449aefcc198bfc68" } -->> { "hash" : "a173b41b16b63a0102175a9e86052afd" } on : shard0001 Timestamp(45, 10)
{ "hash" : "a173b41b16b63a0102175a9e86052afd" } -->> { "hash" : "a30085714610e8796ba21edc42665bf1" } on : shard0001 Timestamp(49, 24)
{ "hash" : "a30085714610e8796ba21edc42665bf1" } -->> { "hash" : "a431f8333c13d93aadc195bb5b77ba7d" } on : shard0001 Timestamp(86, 12)
{ "hash" : "a431f8333c13d93aadc195bb5b77ba7d" } -->> { "hash" : "a54f025a25dfd94a9d2b645c1d4f105a" } on : shard0001 Timestamp(87, 8)
{ "hash" : "a54f025a25dfd94a9d2b645c1d4f105a" } -->> { "hash" : "a8c25e1ed3f156f7bf1b6ac03157b7c2" } on : shard0001 Timestamp(87, 9)
{ "hash" : "a8c25e1ed3f156f7bf1b6ac03157b7c2" } -->> { "hash" : "aa28021b4afb48bd9624017ac9daf801" } on : shard0001 Timestamp(60, 22)
{ "hash" : "aa28021b4afb48bd9624017ac9daf801" } -->> { "hash" : "ab7803bd7d42268f4595e461213b6359" } on : shard0001 Timestamp(76, 10)
{ "hash" : "ab7803bd7d42268f4595e461213b6359" } -->> { "hash" : "acab1ba0757f0fa9a92c37eddd4db966" } on : shard0001 Timestamp(86, 10)
{ "hash" : "acab1ba0757f0fa9a92c37eddd4db966" } -->> { "hash" : "aec8dd8cef8c5228c096615a471843a2" } on : shard0001 Timestamp(86, 11)
{ "hash" : "aec8dd8cef8c5228c096615a471843a2" } -->> { "hash" : "b02fd4a1e43f5f991386583e5b448917" } on : shard0001 Timestamp(60, 20)
{ "hash" : "b02fd4a1e43f5f991386583e5b448917" } -->> { "hash" : "b17f660d7f3a5f814e74054b3d79786c" } on : shard0001 Timestamp(76, 12)
{ "hash" : "b17f660d7f3a5f814e74054b3d79786c" } -->> { "hash" : "b2c9640546e152d22e73ffa8522a751d" } on : shard0001 Timestamp(81, 6)
{ "hash" : "b2c9640546e152d22e73ffa8522a751d" } -->> { "hash" : "b509b2eee0d8dec3798aa861ddbc624e" } on : shard0001 Timestamp(81, 7)
{ "hash" : "b509b2eee0d8dec3798aa861ddbc624e" } -->> { "hash" : "b6ab24b872b93da5c1ddf2ec81b7aad4" } on : shard0004 Timestamp(20, 0)
{ "hash" : "b6ab24b872b93da5c1ddf2ec81b7aad4" } -->> { "hash" : "b84c2a20458a7e4d23f63cacc43059db" } on : shard0005 Timestamp(21, 0)
{ "hash" : "b84c2a20458a7e4d23f63cacc43059db" } -->> { "hash" : "b9ed7189c285195f4b2d97ebf85544a8" } on : shard0006 Timestamp(22, 0)
{ "hash" : "b9ed7189c285195f4b2d97ebf85544a8" } --&g
所以这里是 -
您看到的行为似乎是正常的或接近正常的 MongoDB 分片活动。我将在下面详细解释原因。
默认块大小为 64MB 和 179 个块，总数据大小低于 11GB（即最大 64MB 块时间 179）。它很可能在此之下。
然而，您有 8 个分片——这意味着您已经在大量分片/块中分发了（相对）少量的数据。这会导致数据分布出现一些严重的不均匀性，直到您拥有更多块或减少分片数量以使每个分片拥有更多块后，才会自行解决。
首先，与普遍看法相反，MongoDB 平衡器并没有保持一切精确平衡。它根据某些阈值启动，然后在达到其他阈值时关闭。否则它会不断地颠簸。
阈值可以在这里找到：http : //docs.mongodb.org/manual/core/sharding-balancing/
在您的情况下，如果有超过 80 个块，您将不会迁移，直到最大和最小分片（以块数计）之间的差异至少为 8。您现在的最大差异为 5，在 shard0000 上的 25 个块和 20 个块之间在 shard0006 和 shard00007 上。这说明了一些重要的差异。
请注意，默认平衡器行为不会将差异驱动为 0 - 因此，当您添加新分片时，新分片将以较少的块开始，因为当最大分片和最小分片之间的差异为 2 时迁移停止。
当每个分片有大量块时，这种差异并不那么明显 - 但事实并非如此。因此，这将继续明显，直到每个分片的块集中度更高。
添加较小的新分片后，数据的持续分布取决于您的数据在分片键中的均匀分布程度。基于日期的密钥或其他稳步增加的密钥会产生热点——完全随机的密钥接近于完美均匀的分布。
在查看您当前的分片中的块分布并假设您的迁移平衡到每个分片 2 个块以内（注意这是一个假设 - 它可能在此之前停止并出现错误）看起来您可能有一个不完全随机的哈希关键，因为分布看起来有点偏。
请注意，这是一个“可能” - 可能是由于错误而停止的不完整平衡器运行的工件。
无论如何，您不太可能看到“完美”的平衡。在有足够多的新数据进入之后，您应该会看到更接近的平衡，这样每个分片的总块数是 >> then 阈值。现在，每个分片有 20 - 25 个块，起始阈值为 8 差，停止阈值为 2 差，您将继续看到数据平衡的显着差异，旧的、更大的分片总是保持更大。
在当前的发行版中，你需要一个碎片来击中 28 个块，而另一个碎片在平衡器启动之前位于 20 个块 - 差异为 40%。假设所有块的大小相同 - 将新数据分配给块的任何偏差都会使该数字产生偏差。
如果您在 4 个分片而不是 8 个分片上拥有相同数量的块，则平衡器启动时的差异仅为 20%。所以有大量的分片和少量的块会使这个问题变得更糟。
需要进一步调查的一件事是每个块有多大——通过现有的 MongoDB 工具直接确定并不容易，但有一些代码可能会有所帮助：
https://github.com/comerford/mongodb-scripts/blob/master/AllChunkInfo.js
请注意，我会先在测试中尝试一下。目标是了解您的块大小是否合理，如果不是，为什么不。
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