CQL: SQL In Cassandra

CQL: SQL for Cassandra Cassandra NYC December 6, 2011 Eric Evans eric@acunu.com @jericevans, @acunu

● Overview, history, motivation● Performance characteristics● Coming soon (?)● Drivers status

What?● Cassandra Query Language ● aka CQL ● aka /ˈsēkwəl/● Exactly like SQL (except where its not)● Introduced in Cassandra 0.8.0● Ready for production use

SQL? Almost.–- Inserts or updatesINSERT INTO Standard1 (KEY, col0, col1)VALUES (key, value0, value1) vs.–- Inserts or updatesUPDATE Standard1SET col0=value0, col1=value1 WHERE KEY=key

SQL? Almost.–- Get columns for a rowSELECT col0,col1 FROM Standard1 WHERE KEY=key–- Range of columns for a rowSELECT col0..colN FROM Standard1 WHERE KEY=key–- First 10 results from a range of columnsSELECT FIRST 10 col0..colN FROM Standard1 WHERE KEY=key–- Invert the sorting of resultsSELECT REVERSED col0..colN FROM Standard1 WHERE KEY=key

Interface Instability

(Un)ease of useColumn col = new Column(ByteBuffer.wrap(“name”.getBytes()));col.setValue(ByteBuffer.wrap(“value”.getBytes()));col.setTimestamp(System.currentTimeMillis());ColumnOrSuperColumn cosc = new ColumnOrSuperColumn();cosc.setColumn(col);Mutation mutation = new Mutation();Mutation.setColumnOrSuperColumn(cosc);List mutations = new ArrayList<Mutation>();mutations.add(mutation);Map mutations_map = new HashMap<ByteBuffer, Map<String, List<Mutation>>>();Map cf_map = new HashMap<String, List<Mutation>>();cf_map.set(“Standard1”, mutations);mutations.put(ByteBuffer.wrap(“key”.getBytes()), cf_map)

CQLINSERT INTO Standard1 (KEY, col0) VALUES (key, value0)

Why? How about...● Better stability guarantees● Easier to use (you already know it)● Better code readability / maintainability

Why? How about...● Better stability guarantees● Easier to use (you already know it)● Better code readability / maintainability● Irritates the NoSQL purists

Why? How about...● Better stability guarantees● Easier to use (you already know it)● Better code readability / maintainability● Irritates the NoSQL purists● (Still )irritates the SQL purists

Performance

Thrift RPCColumn col = new Column(ByteBuffer.wrap(“name”.getBytes()));col.setValue(ByteBuffer.wrap(“value”.getBytes()));col.setTimestamp(System.currentTimeMillis());ColumnOrSuperColumn cosc = new ColumnOrSuperColumn();cosc.setColumn(col);Mutation mutation = new Mutation();Mutation.setColumnOrSuperColumn(cosc);List mutations = new ArrayList<Mutation>();mutations.add(mutation);Map mutations_map = new HashMap<ByteBuffer, Map<String, List<Mutation>>>();Map cf_map = new HashMap<String, List<Mutation>>();cf_map.set(“Standard1”, mutations);mutations.put(ByteBuffer.wrap(“key”.getBytes()), cf_map)

Your query, its a graph

CQLINSERT INTO Standard1 (KEY, col0) VALUES (key, value0)

Hotspot Quoted string literalsUPDATE table SET name = value WHERE KEY = somekey

Hotspot Quoted string literalsUPDATE table SET name = value WHERE KEY = somekey● Anything that appears between quotes● Inlined Java constructs a StringBuilder to store the contents (slow not fast)● Incurred multiple times per statement

Hotspot MarshallingUPDATE table SET clear = abffaadd10 WHERE KEY = acfe12ff

Hotspot MarshallingUPDATE table SET clear = abffaadd10 WHERE KEY = acfe12ff ascii blob

Hotspot MarshallingUPDATE table SET clear = abffaadd10 WHERE KEY = acfe12ff ascii blob● Terms are marshalled to bytes by type● String.getBytes is slow (AsciiType)● Hex conversion is fast faster (BytesType)● Incurred multiple times per statement

Hotspot Copying / Conversionexecute_cql_query( ByteBuffer query, enum compression)● Query is binary to support compression (is it worth it?)● And dont forget the String → ByteBuffer conversion on the client-side● Incurred only once per statement!

Achtung! (These tests werent perfect)● Uneeded String → ByteBuffer → String● No query compression implemented● Co-located client and server

Insert 20M rows, 5 columns Avg rate Avg latency RPC 20,953/s 1.6ms CQL 19,176/s (-8%) 1.7ms (+9%)

Insert 10M rows, 5 cols (indexed) Avg rate Avg latency RPC 9,850/s 5.3ms CQL 9,290/s (-6%) 5.5ms (+4%)

Counts, 10M rows, 5 cols Avg rate Avg latency RPC 18,052/s 1.7ms CQL 17,635/s (-2%) 1.7ms

Reading 20M rows, 5 cols Avg rate Avg latency RPC 22.726/s 2.0ms CQL 20,272/s (-11%) 2.3ms (+10%)

In SummaryDont step over dollars to pick up pennies!

Coming Soon(ish)

Roadmap● Prepared statements (CASSANDRA-2475)● Compound columns (CASSANDRA-2474)● Custom transport / protocol (CASSANDRA-2478)● Performance testing (CASSANDRA-2268)● Schema introspection (CASSANDRA-2477)● Multiget support (CASSANDRA-3069)

Drivers

Drivers● Hosted on Apache Extras (Google Code)● Tagged cassandra and cql● Licensed using Apache License 2.0● Conforming to a standard for database connectivity (if applicable)● Coming soon, automated testing and acceptance criteria

DriversDriver Platform Statuscassandra-jdbc Java Goodcassandra-dbapi2 Python Goodcassandra-ruby Ruby Newcassandra-pdo PHP Newcassandra-node Node.js Goodhttp://code.google.com/a/apache-extras.org/hosting/search?q=label%3aCassandra

The End

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CQL: SQL In Cassandra

by Eric Evans

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