cql: sql in cassandra
DESCRIPTION
CQL presentation from Cassandra NYC, December 6, 2011TRANSCRIPT
● Overview, history, motivation
● Performance characteristics
● Coming soon (?)
● Drivers status
What?
● Cassandra Query Language● aka CQL● aka /ˈsēkwəl/
● Exactly like SQL (except where it's 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
Why?
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)
CQL
INSERT 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, it's a graph
CQL
INSERT INTO Standard1 (KEY, col0) VALUES (key, value0)
HotspotQuoted string literals
UPDATE table SET 'name' = 'value' WHERE KEY = 'somekey'
HotspotQuoted string literals
UPDATE table SET 'name' = 'value' WHERE KEY = 'somekey'
HotspotQuoted string literals
UPDATE 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
HotspotMarshalling
UPDATE table SET 'clear' = 'abffaadd10' WHERE KEY = 'acfe12ff'
HotspotMarshalling
UPDATE table SET 'clear' = 'abffaadd10' WHERE KEY = 'acfe12ff'
ascii blob
HotspotMarshalling
UPDATE table SET 'clear' = 'abffaadd10' WHERE KEY = 'acfe12ff'
● Terms are marshalled to bytes by type● String.getBytes is slow (AsciiType)● Hex conversion is fast faster (BytesType)● Incurred multiple times per statement
ascii blob
HotspotCopying / Conversion
execute_cql_query( ByteBuffer query, enum compression)
● Query is binary to support compression (is it worth it?)● And don't forget the String → ByteBuffer conversion on
the client-side● Incurred only once per statement!
Achtung!(These tests weren't 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 Summary
Don't 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
Drivers
Driver Platform Statuscassandra-jdbc Java Goodcassandra-dbapi2 Python Goodcassandra-ruby Ruby Newcassandra-pdo PHP Newcassandra-node Node.js Good
http://code.google.com/a/apache-extras.org/hosting/search?q=label%3aCassandra
The End