replset:SECONDARY> show collections

2015-12-30T19:45:18.149+0900 E QUERY    Error: listCollections failed: { "note" : "from execCommand", "ok" : 0, "errmsg" : "not master" }

replset:SECONDARY> db.customer.find()

Error: error: { "ok" : 0, "errmsg" : "not master and slaveOk=false", "code" : 13435 }

replset:SECONDARY> rs.slaveOk()

replset:SECONDARY> db.customer.find()

....

In MongoDB 3.0, WiredTiger provides three compression options for collections:

• No compression
• Snappy (enabled by default) – very good compression, efficient use of resources
• zlib (similar to gzip) – excellent compression, but more resource intensive

There are two compression options for indexes:

• No compression
• Prefix (enabled by default) – good compression, efficient use of resources

replset:PRIMARY> use <db이름>

replset:PRIMARY> db.stats()

{

"db" : "storypicker",

"collections" : 16,

"objects" : 2706554,

"avgObjSize" : 394.5955794711652,

"dataSize" : 1067994244,

"storageSize" : 659419136,

"numExtents" : 0,

"indexes" : 37,

"indexSize" : 149549056,

"ok" : 1

}

https://blog.nodebb.org/mongodb-3-0-wiredtiger-compression-results/

mongodb 2.6.11 + mmapv1

{
        "ns" : "0.objects",
        "count" : 2668342,
        "size" : 513690384,
        "avgObjSize" : 192,
        "storageSize" : 629637120,
        "totalIndexSize" : 357896224,
        "indexSizes" : {
                "_id_" : 86583840,
                "expireAt_1" : 45654784,
                "_key_1_score_-1" : 109084192,
                "_key_1_value_-1" : 116573408
        }
}

mongodb 3.2.0-rc + wiredtiger

{
        "ns" : "0.objects",
        "count" : 2668337,
        "size" : 345978824,
        "avgObjSize" : 129,
        "storageSize" : 109842432,
        "totalIndexSize" : 97681408,
        "indexSizes" : {
                "_id_" : 24162304,
                "expireAt_1" : 10874880,
                "_key_1_score_-1" : 22380544,
                "_key_1_value_-1" : 40263680
        }
}

To run mongod with the RocksDB storage engine, just invoke mongod with the --storageEngine=rocksdb parameter.  You can add the RocksDB node to an existing replica set by using rs.Add() and performing an initial sync as you normally would.

Please treat this as work in progress. Both of those branches will keep changing as we keep improving the performance and stability.  We will release and package a “stable” version at some point in the future.

MyRocks

As you might know, we’re working hard to integrate RocksDB as a storage engine for MySQL. This project is pretty important for us because we’re heavy users of MySQL. We’re already getting pretty good performance results, but there is more work to be done. We need to focus on both performance and stability. The most high priority items on are list are:

1. Reduce CPU costs of RocksDB as a MySQL storage engine
2. Implement pessimistic concurrency control to support repeatable read isolation level in MyRocks
3. Reduce P99 read latency, which is high mostly because of lingering tombstones
4. Port ZSTD compression

MongoRocks

Another database that we’re working on is MongoDB. The project of integrating MongoDB with RocksDB storage engine is called MongoRocks. It’s already running in production at Parse [1] and we’re seeing surprisingly few issues. Our plans for the next half:

1. Keep improving performance and stability, possibly reuse work done on MyRocks (workloads are pretty similar).
2. Increase internal and external adoption.
3. Support new MongoDB 3.2.

> db.contents.find( {"created_at" : { "$gte":"2014-10-09T13:32:37Z", "$lte":"2014-10-09T13:32:38Z" } } )

> db.contents.find( {"media_type" : {"$in" : ["image", "music"]}})

> db.contents.find( {"media_type" : {"$nin" : ["image", "music"]}})

> db.contents.find( { "comments" : null } )