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MySQL can handle at least some aspects of such. At 15TB, disk I/O is the number one problem! Both on INSERT and SELECT. Indexes are BTree structured. This gives "close to instantaneous" fetching of one row, given the index. It also gives rapid scanning in the BTree order, forward or backward. You can have multiple unrelated indexes, but it is ...


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As part of the MongoDB 3.0 upgrade it is strongly recommended that you upgrade to the SCRAM-SHA-1 authentication scheme. New users will have their credentials created in this format by default; mixed authentication schemas will likely lead to confusion. You will need to upgrade your client driver & admin tools (if you're using a GUI) in order to use the ...


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The current wording in the documented steps may be somewhat confusing given the relative references to first/last/second config servers. I've added some context for the documented steps below, but you should consider the manual the definitive source. It's also worth noting that you do not have to upgrade the config servers to use WiredTiger (even if your ...


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You can perform a rolling upgrade of your replica set from MongoDB 2.6 to 3.0. While a mixed version 2.6/3.0 replica set is supported for the purposes of upgrading, you should not run with this configuration for longer than is required. You should also read the 3.0 upgrade and compatibility change notes carefully, as important considerations will be ...


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It will work for conditional $set update operation http://docs.mongodb.org/manual/reference/operator/update/setOnInsert/ db.products.update( { _id: 1 }, { $set: { item: "apple" }, $setOnInsert: { defaultQty: 100 } }, {upsert: true } ) Here setOnInsert will set defaultQty only when a new record is inserted. Both $set and $setOnInsert can ...


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Question 1: The answer here is yes and no. In a replica set if your PRIMARY fails one of your SECONDARIES will take charge. If all CRUD statements have replicated from PRI to SEC when your disk crash then you are fine. But in case that some statements are not (replication lag) and your disk crash you will lose those statements. If you can handle that loss ...


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The solution to this issue was as follows: Starting with the secondary: Inside of Mongo I ran the following: db.shutdownServer() exit On the command line: rm -rf /var/lib/mongodb/* sudo service mongodb start It then takes a couple of hours to resync. Once resynced I did the following on the primary: rs.status() //To make sure that the everything was ...


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No, MongoDB does not support two-way synchronization. It has master-slave replication, where all writes must occur on the master node before being replicated to the slave nodes. You can read about all the replication capabilities of MongoDB in their documentation.


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Number of collection is equal 2: The 2 collections are the system.indexes system.users. Execute the "show collections" command under your database to confirm. Filesize: MongoDB allocates "physical files" or files on disk per database. For example eventsdb.0, eventsdb.1 ... Collections are stored with a distributed way within these files. Dropping a ...


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For your use case of key-value data, where the value is simple, MongoDB is more than you need. It is a document-oriented data store for complex value types. A specific key-value store would suit your needs. RIAK is the one I've looked at though several others exist. Since your retrieval will be by time range i.e. key range, Elastic's full-text ...


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You can verify that no migrations are running by checking the balance with sh.isBalancerRunning() which is true if chunks are being migrated and false if not. Using BalancerState only shows you if it is enabled or disabled, not its current run state. While it depends on what the specific documentation says, I'd probably feel safer setting the balancer ...


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My field avgObjSize was around 6442 bytes. I chose a random document in my collection, I typed : Object.bsonsize(db.collectionName.find({"_id" : ObjectId("5508497c51a990da07b07106")})) And I obtained 810 bytes. Why do I have this huge difference ? The db.collection.find() method returns a cursor, so what you have calculated is the ...


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It looks like the current MongoDB 3.0 upgrade instructions are missing mention of two important parameters for backing up and restoring users and roles: mongodump --dumpDbUsersAndRoles (see also: Required Access to Backup User Data). mongorestore --restoreDbUsersAndRoles (see also: Required Access to Restore User Data) I can think of several approaches ...


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Upgrade Requirements To upgrade an existing MongoDB deployment to 3.0, you must be running 2.6. If you’re running a version of MongoDB before 2.6, you must upgrade to 2.6 before upgrading to 3.0. See Upgrade MongoDB to 2.6 for the procedure to upgrade from 2.4 to 2.6. Once upgraded to MongoDB 2.6, you cannot downgrade to any version earlier than MongoDB 2.4. ...


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The normal rules of replica set elections apply. If your shard is backed by a 3-node replica set, then you can have any single node down while still being able to maintain a primary. A strict majority of nodes must be available, so 2/3 in the 3-node example. If the data-bearing server you are planning to restart happens to be a replica set primary, I would ...



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