ToroDB: Next Generation Java, MongoDB-compatible, NoSQL & SQL Database

transcript

ToroDB:

Next Generation JavaMongoDB compatible

NoSQL & SQL Database

Álvaro Hernández <aht@torodb.com>

ToroDB @NoSQLonSQL

About *8Kdata*

● Research & Development in databases

● Consulting, Training and Support in PostgreSQL

● Java Developers, JavaSpecialists.eu, JCrete.org

● About myself: CTO at 8Kdata:@ahachetehttp://linkd.in/1jhvzQ3

www.8kdata.com

ToroDB @NoSQLonSQL

Say you want…

A database with:

● Great functionality

● Consistency (ACID)

● Reliability

● SQL

ToroDB @NoSQLonSQL

… and then also want

A database with:

● NoSQL(MongoDB)

● “Schema-less”

● Scalability

ToroDB @NoSQLonSQL

Fear no more!You can now

have both SQL and NoSQL!

ToroDB @NoSQLonSQL

ToroDB in one slide

● Document-oriented, JSON, NoSQL db

● Open source (AGPL). Written in Java

● MongoDB compatibility (wire protocol level)

● Uses PostgreSQL as a storage backend

ToroDB @NoSQLonSQL

Mapping unstructured datato relational

ToroDB @NoSQLonSQL

ToroDB storage internals

{ "name": "ToroDB", "data": { "a": 42, "b": "hello world!" }, "nested": { "j": 42, "deeper": { "a": 21, "b": "hello" } }}

ToroDB @NoSQLonSQL

The document is split into the following subdocuments:

{ "name": "ToroDB", "data": {}, "nested": {} }

{ "a": 42, "b": "hello world!"}

{ "j": 42, "deeper": {}}

{ "a": 21, "b": "hello"}

ToroDB @NoSQLonSQL

select * from demo.t_3┌─────┬───────┬────────────────────────────┬────────┐│ did │ index │ _id │ name │├─────┼───────┼────────────────────────────┼────────┤│ 0 │ ¤ │ \x5451a07de7032d23a908576d │ ToroDB │└─────┴───────┴────────────────────────────┴────────┘select * from demo.t_1┌─────┬───────┬────┬──────────────┐│ did │ index │ a │ b │├─────┼───────┼────┼──────────────┤│ 0 │ ¤ │ 42 │ hello world! ││ 0 │ 1 │ 21 │ hello │└─────┴───────┴────┴──────────────┘select * from demo.t_2┌─────┬───────┬────┐│ did │ index │ j │├─────┼───────┼────┤│ 0 │ ¤ │ 42 │└─────┴───────┴────┘

ToroDB @NoSQLonSQL

select * from demo.structures┌─────┬────────────────────────────────────────────────────────────────────────────┐│ sid │ _structure │├─────┼────────────────────────────────────────────────────────────────────────────┤│ 0 │ {"t": 3, "data": {"t": 1}, "nested": {"t": 2, "deeper": {"i": 1, "t": 1}}} │└─────┴────────────────────────────────────────────────────────────────────────────┘

select * from demo.root;┌─────┬─────┐│ did │ sid │├─────┼─────┤│ 0 │ 0 │└─────┴─────┘

ToroDB @NoSQLonSQL

How data is stored in schema-less

Data normalization

ToroDB @NoSQLonSQL

This is how we store in ToroDB

ToroDB @NoSQLonSQL

Advantages over MongoDB

ToroDB @NoSQLonSQL

ToroDB: native SQL

ToroDB @NoSQLonSQL

Mix-and-match relational & NoSQL

● Use the same database for both your relational data and ToroDB

● Just use separate schemas (if you will)

● Don't write to ToroDB data or metadata tables

● Query with SQL, do joins, whatever!

ToroDB @NoSQLonSQL

Atomic operations

● There is no support for atomic bulk insert/update/delete operations

● Not even with $isolated:“Prevents a write operation that affects multiple documents from yielding to other reads or writes […] You can ensure that no client sees the changes until the operation completes or errors out. The $isolated isolation operator does not provide “all-or-nothing” atomicity for write operations.”http://docs.mongodb.org/manual/reference/operator/update/isolated/

ToroDB @NoSQLonSQL

“Clean” reads

Oh really?

ToroDB @NoSQLonSQL

“Clean” readshttp://docs.mongodb.org/manual/reference/write-concern/#read-isolation-behavior

“MongoDB will allow clients to read the results of a write operation before the write operation returns.”

“If the mongod terminates before the journal commits, even if a write returns successfully, queries may have read data that will not exist after the mongod restarts.”

Thus, MongoDB suffers from dirty reads. But let's call them just “tainted reads”.

ToroDB @NoSQLonSQL

“Clean” reads

What about $snapshot? Nope:

“The snapshot() does not guarantee that the data returned by the query will reflect a single moment in time nor does it provide isolation from insert or delete operations.”

http://docs.mongodb.org/manual/faq/developers/#faq-developers-isolate-cursors

Cursors in ToroDB run in repeatable read, read-only mode:globalCursorDataSource.setTransactionIsolation("TRANSACTION_REPEATABLE_READ"); globalCursorDataSource.setReadOnly(true);

ToroDB @NoSQLonSQL

Replication&

Horizontal scalability(aka sharding)

ToroDB @NoSQLonSQL

ToroDB v0.4

● ToroDB works as a secondary slave of a MongoDB master (or slave, chained rep)

● Implements the full replication protocol (not as an oplog tailable query)

● Replicates from Mongo to a PostgreSQL

ToroDB @NoSQLonSQL

Write scalability(sharding)

● MongoDB's sharding API not implemented yet (roadmap: ToroDB 0.8)

● Will use MongoDB's mongos without modification, as well as config servers

● Currently we implement sharding at the db level, using backends such as Greenplum

ToroDB @NoSQLonSQL

ToroDBThe software

ToroDB @NoSQLonSQL

The software

Written in Java. v0.40 requires Java7, 1.0 will require 8.

Tested with Oracle and IBM JVMs.Anyone from Azul here today? ;)

Distributed as a JAR file (actually, wrapped with shell executables). Future: also EAR to deploy.

ToroDB @NoSQLonSQL

Standing on the shoulders of giants

And also PostgreSQL, Greenplum, JDBC

ToroDB @NoSQLonSQL

Very modular source code

● The app: 20+ modules (Maven)

● Some of them are individually reusable

● Several abstraction layers:➔ D2R (Document 2 Relational)➔ KVDocument (KV docs abstraction)➔ Database/backend (relational)

ToroDB @NoSQLonSQL

MongoWP

● MongoWP is our implementation of MongoDB's wire protocol

● Based on Netty, an excellent, async and high performance NIO framework

● Callback interface for any MongoDB-based “middleware” implementation (ToroDB, proxy...)

ToroDB @NoSQLonSQL

Architecture

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Executor engines

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Performance

ToroDB @NoSQLonSQL

●Amazon c3.8xlarge➔32 virtual CPUs➔60 GB RAM➔2 x 320 GB SSD

●YCSB 0.5.0, only inserts, 10 minutes● WriteConcern {w:1, fsync: true}● Batch size 1000, 1 and 4 threads● MongoDB 3.2 WiredTiger● ToroDB 0.40 Oracle Java 8, PostgreSQL 9.5 (shared_buffers: 15GB, effective_cache: 45GB)

OLTP Benchmark: YCSB

ToroDB @NoSQLonSQL

OLTP Benchmark: YCSB

ToroDB @NoSQLonSQL

● Amazon reviews datasetImage-based recommendations on styles and substitutesJ. McAuley, C. Targett, J. Shi, A. van den HengelSIGIR, 2015

● AWS c4.xlarge (4vCPU, 8GB RAM) 4KIOPS SSD EBS

● 4x shards, 3x config; 4x segments GP

● 83M records, 65GB plain json

Data Analytics Benchmark

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Disk usage

Mongo 3.0, WT, SnappyGP columnar, zlib level 9

table size index size total size0

10000000000

20000000000

30000000000

40000000000

50000000000

60000000000

70000000000

80000000000

Storage requirements

MongoDB vs ToroDB on Greenplum

ToroDB on GP

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SELECT count( distinct( "reviewerID" ))FROM reviews;

Queries: which one is easier?

db.reviews.aggregate([{ $group: { _id: "reviewerID"}},{ $group: {_id: 1, count: { $sum: 1}}}])

ToroDB @NoSQLonSQL

SELECT "reviewerName", count(*) as reviews FROM reviews GROUP BY "reviewerName" ORDER BY reviews DESC LIMIT 10;

Queries: which one is easier?

db.reviews.aggregate([ { $group : { _id : '$reviewerName', r : { $sum : 1 } } }, { $sort : { r : -1 } }, { $limit : 10 } ], {allowDiskUse: true})

ToroDB @NoSQLonSQL

Query times

3 different queriesQ3 on MongoDB: aggregate fails

27.95 74.87 00

9691007

035 13 31

Query duration (s)

MongoDB vs ToroDB on Greenplum

MongoDB

ToroDB on GP

speedup

ToroDB @NoSQLonSQL

Tips & TricksLessons Learned

ToroDB @NoSQLonSQL

●Lots of type and value for each of those types to manage: strings, integers, Arrays

●Lots of case we have to handle in the code:➔transformation from document to table data structure

➔transformation to internal query lang➔...

Visitor pattern for document manipulation

ToroDB @NoSQLonSQL

●Smaller methods●Somewhere in the deepest class you can see a huge if {} else if {} ... else {}

●Safely add new types

Visitor pattern for document manipulation

Compiler will tell us if we forget to implement some visitor

ToroDB @NoSQLonSQL

Oracle Java Mission Control.●Great tool in general, low impact on perf. Gives A LOT of information on memory allocation, exceptions thrown, etc

●But quite bad to measure the time spent on methods, as it ignores time spent in native code and IO

●Very coarse-grained

Used tools to monitor performance

ToroDB @NoSQLonSQL

VisualVM●Very fine grained●By Default measures time spent on native code and IO

●Impact on performance:➔Configurable, but high in general➔The performance impact seems to be heterogeneous (some methods are more penalized than others)

Used tools to monitor performance

ToroDB @NoSQLonSQL

● ToroDB uses HashMaps. Keys are the JSON keys● When there is a lookup on a HashMap, the equals must be executed.

● Each key is a String and String#equals is O(1) when both Strings are the same, but O(n) when both Strings are equal but not the same object.

● As a result, we were spending much more time than expected looking for on HashMaps

● We use a pool of keys that guarantees that if two keys equal, they are the same object.

● Cons: Some time is spent on the pool of keys, as they are basically a map.

Document keys & maps

ToroDB @NoSQLonSQL

● ToroDB has to deal with memory pressure when the MongoDB clients produce requests faster than the SQL backend can handle them.

● This is specially important when the client is using the async drivers

● Ideal solution: Make the backend faster● Specially adding async behaviour● But it requires a new non-JDBC driver => Phoebe● Practical solution: To use a back pressure mechanism to make the client be as fast as the backend can be.

Dealing with Memory Pressure

ToroDB @NoSQLonSQL

● It is important to monitor the hotspots● We found some parts of our code that were correct, but very inefficient.➔Some of them were errors (some analysis that were executed twice on different parts of the code)

➔Some operations that we considered faster enough were executed so many times that it was critical to reimplement on a more performant way

Chasing performance problems

ToroDB @NoSQLonSQL

Download, clone, PR, star it!

https://github.com/torodb/torodb

Check our FAQ:

https://github.com/torodb/torodb/wiki/FAQ

ToroDB @NoSQLonSQL

ToroDB: Next Generation Java, MongoDB-compatible, NoSQL & SQL Database

Software