Introduction to.ppt

1、Introduction toApache Cassandra,(for Java developers!),Nate McCall zznate,Brief Intro,NOT a key/value store Columns are dynamic inside a column family SSTables are immutable SSTables merged on reads All nodes share the same role (i.e. no single point of failure) Trading ACID compliance for scalabili

2、ty is a fundamental design decision,How does this impact development?,Substantially. For operations affecting the same data, that data will become consistent eventually as determined by the timestamps. But you can trade availability for consistency. (More on this later) You can store whatever you wa

3、nt. Its all just bytes. You need to think about how you will query the data before you write it.,Neat. So Now What?,Like any database, you need a client! Python: Telephus: Pycassa: Java: Hector: Pelops: Kundera Datanucleus JDO: Grails: grails-cassandra: .NET: FluentCassandra: Aquiles: Ruby: Cassandr

4、a: PHP: phpcassa: SimpleCassie:,. but do not roll your own,Thrift,Fast, efficient serialization and network IO. Lots of clients available (you can probably use it in other places as well) Why you dont want to work with the Thrift API directly: SuperColumn ColumnOrSuperColumn ColumnParent.super_colum

5、n ColumnPath.super_column Map mutationMap,Higher Level Client,Hector JMX Counters Add/remove hosts: automatically programatically via JMX Plugable load balancing Complete encapsulation of Thrift API Type-safe approach to dealing with Apache Cassandra Lightweight ORM (supports JPA 1.0 annotations) Ma

6、venized!/maven2/me/prettyprint/,CQL,Currently in Apache Cassandra trunk Experimental Lots of possibilities fromtest/system/test_cql.py: UPDATE StandardLong1 SET 1L=1, 2L=2, 3L=3, 4L=4 WHERE KEY=aa SELECT cd1, col FROM Standard1 WHERE KEY = kd DELETE cd1, col FROM Standard1 WHERE

7、 KEY = kd,Avro?,Gone. Added too much complexity after Thrift caught up. None of the libraries distinguished themselves as being a particularly crappy choice for serialization. (SeeCASSANDRA-1765),Thrift API Methods,Retrieving Writing/Removing Meta Information Schema Manipulation,Thrift API Methods -

8、 Retrieving,get: retrieve a single column for a key get_slice: retrieve a slice of columns for a key multiget_slice: retrieve a slice of columns for a list of keys get_count: counts the columns of key (you have to deserialize the row to do it) get_range_slices: retrieve a slice for a range of keys g

9、et_indexed_slices (FTW!),Thrift API Methods - Writing/Removing,insert batch_mutate (batch insertion AND deletion) remove truncate*,Thrift API Methods - Meta Information,describe_cluster_name describe_version describe_keyspace describe_keyspaces,Thrift API Methods - Schema,system_add_keyspace system_

10、update_keyspace system_drop_keyspace system_add_column_family system_update_column_family system_drop_column_family,vs. RDBMS - Consistency Level,Consistency istunable per request! Cassandra provides consistency when R + W N (read replica count +write replica count replication factor). * CONSITENCY

11、LEVEL FAILURE IS NOT A ROLLBACK* Idempotent: an operation can be applied multiple times without changing the result,vs. RDBMS - Append Only,Proper data modelling will minimizes seeks (Go to Tylers presentation for more!),On to the Code., Uses Maven. Really basic. Modify/abuse/alter as needed. Descri

12、ptions of what is going on and how to run each example are in the Javadoc comments. Sample data is based on North American Numbering Plan /wiki/North_American_Numbering_Plan,Data Shape,512 202 30.27 097.74 W TX Austin 512 203 30.27 097.74 L TX Austin 512 204 30.32 097.73 W TX A

13、ustin 512 205 30.32 097.73 W TX Austin 512 206 30.32 097.73 L TX Austin,Get a Single Column for a Key,GetCityForNpanxx.java Retrieve a single column with: Name Value Timestamp TTL,Get the Contents of a Row,GetSliceForNpanxx.java Retrieves a list of columns (Hector wraps these in a ColumnSlice) Slice

14、Predicate can either be explicit set of columns OR a range (more on ranges soon) Another messy either/or choice encapsulated by Hector,Get the (sorted!) Columns of a Row,GetSliceForStateCity.java Shows why the choice of comparator is important (this is the order in which the columns hit the disk - t

15、ake advantage of it) Can be easily modified to return results in reverse order (but this is slightly slower),Get the Same Slice from Several Rows,MultigetSliceForNpanxx.java Very similar to get_slice examples, except we provide a list of keys,Get Slices From a Range of Rows,GetRangeSlicesForStateCit

16、y.java Like multiget_slice, except we can specify a KeyRange (encapsulated by RangeSlicesQuery#setKeys(start, end) The results of this query will be significantly more meaningful with OrderPreservingPartitioner (try this at home!),Get Slices From a Range of Rows - 2,GetSliceForAreaCodeCity.java Comp

17、ound column name for controlling ranges Comparator at work on text field,Get Slices from Indexed Columns,GetIndexedSlicesForCityState.java You only need to index a single column to apply clauses on other columns (BUT- the indexed column must be present with an EQUALS clause!) (Its just another Colum

18、nFamily maintained automatically),Insert, Update and Delete,. are effectively the same operation. InsertRowsForColumnFamilies.java DeleteRowsForColumnFamily.java Run each in succession (in whichever combination you like) and verify your results on the CLI Hint: watch the timestamps bin/cassandra-cli

19、 -host localhost use Tutorial; list AreaCode; list Npanxx; list StateCity;,Stuff I Punted on for the Sake of Brevity,meta_* methods CassandraClusterTest.java: L43-81 hector system_* methods SchemaManipulation.java hector-examples CassandraClusterTest.java: L84-157 hector ORM (it works and is in production) ORM Documentation multiple nodes failure scenarios Data modelling (go see Tylers presentation),Things to Remember,deletes and timestamp granularity range ghosts u