Discussion:
2.4 & 2.6: Will a write concern >1 reverse primary write when Oplog write fails?
(too old to reply)
David Ffrench
2018-12-03 10:38:38 UTC
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*Hi All,Any insight on this would be greatly appreciated. I know it is on a
much older version of Mongo as well, using MongoDB 2.4.The Problem 1. Write
to primary replica set member - Successful2. Write to Oplog - Fails3. Write
to secondary replica set members - Fails- Never happens due to no Oplog
entry4. Secondary becomes Primary - Data loss for this write- Since the
document does not exist on the secondary, when it becomes the primary, my
interpretation is this data will be lost.- The below error is returned due
to the Oplog write failure but the write persists on the primary.Error
returnedWriteConcernError(passes >= maxPasses in
NamespaceDetails::cappedAlloc: ns: local.oplog.rs, len: 461696, maxPasses:
15391, _maxDocsInCapped: 2147483647, nrecords: 820038, datasize:
2478185272)Related JIRA - https://jira.mongodb.org/browse/SERVER-6981
<https://jira.mongodb.org/browse/SERVER-6981>Question*
*Will setting a write concern of > 1 reverse the replica set primary write
when Oplog write fails?*


*If you think my understanding is incorrect or have any details on this,
any help would be greatly appreciated.*

*Thanks,*

*David*
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'Kevin Adistambha' via mongodb-user
2018-12-04 23:36:28 UTC
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Hi David,

Although 2.4 & 2.6 are out of support and is strongly not recommended to be
used in a production environment anymore, I will try to answer as best I
can:

The root cause of that error is SERVER-12058
<https://jira.mongodb.org/browse/SERVER-12058>, so changing the
WriteConcern setting will not do much. The root issue itself was fixed in
June 2014 in MongoDB 2.6.6, so I would assume that you’re using an even
older version than this. For a detailed technical explanation of the issue
you’re seeing, please see SERVER-17561
<https://jira.mongodb.org/browse/SERVER-17561>.

Note that the current version of MongoDB is 4.0.4, where it contains many
improvements due to years of engineering effort, so if it is possible, I
would recommend you to consider upgrading to a supported version of MongoDB
<https://www.mongodb.com/support-policy> instead.

Best regards,
Kevin
​
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David Ffrench
2018-12-05 14:18:34 UTC
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Thank you very much Kevin. Your reply has been immensely helpful.
Post by 'Kevin Adistambha' via mongodb-user
Hi David,
Although 2.4 & 2.6 are out of support and is strongly not recommended to
be used in a production environment anymore, I will try to answer as best I
The root cause of that error is SERVER-12058
<https://jira.mongodb.org/browse/SERVER-12058>, so changing the
WriteConcern setting will not do much. The root issue itself was fixed in
June 2014 in MongoDB 2.6.6, so I would assume that you’re using an even
older version than this. For a detailed technical explanation of the issue
you’re seeing, please see SERVER-17561
<https://jira.mongodb.org/browse/SERVER-17561>.
Note that the current version of MongoDB is 4.0.4, where it contains many
improvements due to years of engineering effort, so if it is possible, I
would recommend you to consider upgrading to a supported version of
MongoDB <https://www.mongodb.com/support-policy> instead.
Best regards,
Kevin
​
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