MongoDB 3.0 storage engine api and wired tiger.

1. Introduction to new high performance
storage engines in MongoDB 2.8
Henrik Ingo
Solutions Architect, MongoDB
3.0

2. 2
Hi, I am Henrik Ingo
@h_ingo

3. Introduction to new high performance
storage engines in MongoDB 2.8
Agenda:
- MongoDB and NoSQL
- Storage Engine API
- WiredTiger configuration + performance
3.0

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Most popular NoSQL database

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5 NoSQL categories
Key Value Wide Column Document
Graph Map Reduce
Redis, Riak Cassandra
Neo4j Hadoop

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MongoDB is a Document Database
MongoDB
Rich Queries
• Find Paul’s cars
• Find everybody in London with a car
built between 1970 and 1980
Geospatial
• Find all of the car owners within 5km of
Trafalgar Sq.
Text Search
• Find all the cars described as having
leather seats
Aggregation
• Calculate the average value of Paul’s
car collection
Map Reduce
• What is the ownership pattern of colors
by geography over time? (is purple
trending up in China?)
{
first_name: ‘Paul’,
surname: ‘Miller’,
city: ‘London’,
location:
[45.123,47.232],
cars: [
{ model: ‘Bentley’,
year: 1973,
value: 100000, … },
{ model: ‘Rolls Royce’,
year: 1965,
value: 330000, … }
}
}

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Operational Database Landscape

8. MongoDB 3.0 & storage engines

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Current state in MongoDB 2.6
Read-heavy apps
• Great performance
• B-tree
• Low overhead
• Good scale-out perf
• Secondary reads
• Sharding
Write-heavy apps
• Good scale-out perf
• Sharding
• Per-node efficiency wish-list:
• Doc level locking
• Write-optimized data
structures (LSM)
• Compression
Other
• Complex transactions
• In-memory engine
• SSD optimized engine
• etc...

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Current state in MongoDB 2.6
Read-heavy apps
• Great performance
• B-tree
• Low overhead
• Good scale-out perf
• Secondary reads
• Sharding
Write-heavy apps
• Good scale-out perf
• Sharding
• Per-node efficiency wish-list:
• Doc level locking
• Write-optimized data
structures (LSM)
• Compression
Other
• Complex transactions
• In-memory engine
• SSD optimized engine
• etc...
How to get all of the above?

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MongoDB 3.0 Storage Engine API
MMAP
Read-heavy app
WiredTiger
Write-heavy app
3rd party
Special app

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MMAP
Read-heavy app
WiredTiger
Write-heavy app
3rd party
Special app
• One at a time:
– Many engines built into mongod
– Choose 1 at startup
– All data stored by the same engine
– Incompatible on-disk data formats (obviously)
– Compatible client API
• Compatible Oplog & Replication
– Same replica set can mix different engines
– No-downtime migration possible
MongoDB 3.0 Storage Engine API

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• MMAPv1
– Improved MMAP (collection-level locking)
• WiredTiger
– Discussed next
• RocksDB
– LSM style engine developed by Facebook
– Based on LevelDB
• TokuMXse
– Fractal Tree indexing engine from Tokutek
Some existing engines

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• Heap
– In-memory engine
• Devnull
– Write all data to /dev/null
– Based on idea from famous flash animation...
– Oplog stored as normal
• SSD optimized engine (e.g. Fusion-IO)
• KV simple key-value engine
Some rumored engines
https://github.com/mongodb/mongo/tree/master/src/mongo/db/storage

15. WiredTiger

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• Modern NoSQL database engine
– flexible schema
• Advanced database engine
– Secondary indexes, MVCC, non-locking algorithms
– Multi-statement transactions (not in MongoDB 3.0)
• Very modular, tunable
– Btree, LSM and columnar indexes
– Snappy, Zlib, 3rd-party compression
– Index prefix compression, etc...
• Built by creators of BerkeleyDB
• Acquired by MongoDB in 2014
• source.wiredtiger.com
What is WiredTiger

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Choosing WiredTiger at server startup
mongod --storageEngine wiredTiger
http://docs.mongodb.org/master/reference/program/mongod/#cmdoption--storageEngine

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Main tunables exposed as MongoDB options
mongod --storageEngine wiredTiger
--wiredTigerCacheSizeGB 8
--wiredTigerDirectoryForIndexes /data/indexes
--wiredTigerCollectionBlockCompressor zlib
--dbpath /data/datafiles
http://docs.mongodb.org/master/reference/program/mongod/#cmdoption--storageEngine

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All WiredTiger options via configString (hidden)
mongod --storageEngine wiredTiger
--wiredTigerEngineConfigString
"cache_size=8GB,eviction=(threads_min=4,threads_max=8),
checkpoint(wait=30)"
--wiredTigerCollectionConfigString
"block_compressor=zlib"
--wiredTigerIndexConfigString
"type=lsm,block_compressor=zlib"
--wiredTigerDirectoryForIndexes /data/indexes
See docs for wiredtiger_open() & WT_SESSION::create()
http://source.wiredtiger.com/2.5.0/group__wt.html#ga9e6adae3fc6964ef837a62795c7840ed
http://source.wiredtiger.com/2.5.0/struct_w_t___s_e_s_s_i_o_n.html#a358ca4141d59c345f401c58501276bbb

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Also via createCollection(), createIndex()
db.createCollection( "users",
{ storageEngine: {
wiredTiger: {
configString: "block_compressor=none" }
}
)
http://docs.mongodb.org/master/reference/method/db.createCollection/#db.createCollection
http://docs.mongodb.org/master/reference/method/db.collection.createIndex/#db.collection.createIndex

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• db.serverStatus()
• db.collection.stats()
More...

22. Understanding and Optimizing
WiredTiger

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Understanding WiredTiger architectureWiredTigerSE
Btree LSM Columnar
Cache (default: 50%)
None Snappy Zlib
OS Disk Cache (Default: 50%)
Physical disk

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Covering 90% of your optimization needsWiredTigerSE
Btree LSM Columnar
Cache (default: 50%)
None Snappy Zlib
OS Disk Cache (Default: 50%)
Physical disk
Decompression time
Disk seek time

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Strategy 1: fit working set in CacheWiredTigerSE
Btree LSM Columnar
Cache (default: 50%)
None Snappy Zlib
OS Disk Cache (Default: 50%)
Physical disk
cache_size = 80%

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Strategy 2: fit working set in OS Disk CacheWiredTigerSE
Btree LSM Columnar
Cache (default: 50%)
None Snappy Zlib
OS Disk Cache (Default: 50%)
Physical disk
cache_size = 10%
OS Disk Cache (Remaining: 90%)

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Strategy 3: SSD disk + compression to save €WiredTigerSE
Btree LSM Columnar
Cache (default: 50%)
None Snappy Zlib
OS Disk Cache (Default: 50%)
Physical diskSSD

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Strategy 4: SSD disk (no compression)WiredTigerSE
Btree LSM Columnar
Cache (default: 50%)
None Snappy Zlib
OS Disk Cache (Default: 50%)
Physical diskSSD

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What problem is solved by LSM indexes?Performance
Fast reads Fast writesBoth
Easy:
Add indexes
Easy:
No indexes
Hard:
Smart schema design (hire a consultant)
LSM index structures (or columnar)

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2B inserts (with 3 secondary indexes)
http://smalldatum.blogspot.fi/2014/12/read-modify-write-optimized.html