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  1. Core Server
  2. SERVER-24231

DuplicateKey exeception while replaying the Oplog with unique index

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    • Type: Icon: Bug Bug
    • Resolution: Duplicate
    • Priority: Icon: Major - P3 Major - P3
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      #!/bin/sh
pkill mongod
sleep 5
mkdir db1
rm -rf db1/* db1_backup/ dump/
mongod --dbpath ./db1 --fork --syslog --replSet test
sleep 2

# initializing the db
mongo --eval 'rs.initiate()' && sleep 2
mongo --eval 'db.getCollection("test").createIndex({a: 1}, {unique: true})'
mongo --eval 'db.getCollection("test").insert({a: 1})'
mongo --eval 'db.getCollection("test").update({a: 1}, {$set: {a: 2}})'
mongo --eval 'db.getCollection("test").remove({a: 2})'
mongo --eval 'db.getCollection("test").insert({a: 2})'

# let's perform a point in time restore using the oplog now
mongodump -d local -c oplog.rs
mv dump/local/oplog.rs.bson dump/oplog.bson
rm -rf dump/local

mongorestore --oplogReplay
# failed: restore error: error applying oplog: applyOps: E11000 duplicate key error collection: test.test index: a_1 dup key: { : 2.0 }
      Show
      #!/bin/sh pkill mongod sleep 5 mkdir db1 rm -rf db1/* db1_backup/ dump/ mongod --dbpath ./db1 --fork --syslog --replSet test sleep 2 # initializing the db mongo --eval 'rs.initiate()' && sleep 2 mongo --eval 'db.getCollection( "test" ).createIndex({a: 1}, {unique: true })' mongo --eval 'db.getCollection( "test" ).insert({a: 1})' mongo --eval 'db.getCollection( "test" ).update({a: 1}, {$set: {a: 2}})' mongo --eval 'db.getCollection( "test" ).remove({a: 2})' mongo --eval 'db.getCollection( "test" ).insert({a: 2})' # let's perform a point in time restore using the oplog now mongodump -d local -c oplog.rs mv dump/local/oplog.rs.bson dump/oplog.bson rm -rf dump/local mongorestore --oplogReplay # failed: restore error: error applying oplog: applyOps: E11000 duplicate key error collection: test.test index: a_1 dup key: { : 2.0 }

      While performing the applyOps command, duplicateKey exception are ignored during insertion but not on update operations.

      This could result in a situation where oplog would not be idempotent with a unique index as update could fail where they should not. For example:

      db.test.createIndex({a: 1}, {unique: true})
db.test.insert({a: 1})
db.test.update({a: 1}, {$set: {a: 2, b: 1}})
db.test.remove({a: 2})
db.test.insert({a: 2})

      if you replay all oplog entries whereas the last insert has already been done ({a: 2} is present in the collection), mongod will fail with:

      db.test.update({a: 1}, {$set: {a: 2}})
applyOps: E11000 duplicate key error collection: test.test index: a_1 dup key: { : 2.0 }

      This is specially painful while you are performing point in time restore as mongorestore is stopping at the first error encountered.

      Cheers,
      Damien

        1. replay.sh
          0.9 kB
          Damien Gasparina

            Assignee:
            Unassigned Unassigned
            Reporter:
            damien.gasparina Damien Gasparina
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              Created:
              Updated:
              Resolved: