Apache Cassandra Learning Step by Step (3): Samples ABC

xiu12

　　====16 Feb 2012, by Bright Zheng (IT进行时)====
4. Samples ABC
Wetry to learn it step by step to understand the concepts and Java API usages bymeans of:
1. Concept Introduction
2. CLI
3. Java Sample Code
4.1. Get a Single Column by a Key
4.1.1. Sample Code

public QueryResult<HColumn<String,String>>execute() {                ColumnQuery<String, String,String> columnQuery = HFactory.createStringColumnQuery(keyspace);         columnQuery.setColumnFamily("Npanxx");         columnQuery.setKey("512204");         columnQuery.setName("city");         QueryResult<HColumn<String,String>> result = columnQuery.execute();                 returnresult;     }

4.1.2.  Sample Code runby Maven

C:\projects_learning\learning-cassandra-tutorial>mvn-e exec:java -Dexec.args="get" -Dexec.mainClass="com.datastax.tutorial.TutorialRunner"

The output is:
[INFO] --- exec-maven-plugin:1.1.2-Beta1:java(default-cli) @ cassandra-tutorial ---
HColumn(city=Austin)
[INFO]------------------------------------------------------------------------
[INFO] BUILD SUCCESS
4.1.3.  CLI

[default@Tutorial] get Npanxx['512204']['city']; => (column=city, value=Austin, timestamp=1329234388328000) Elapsed time: 16 msec(s).

4.2. Get multiple columns by a Key
4.2.1. Sample Code

publicQueryResult<ColumnSlice<Long,String>> execute() {         SliceQuery<String, Long,String> sliceQuery =             HFactory.createSliceQuery(keyspace, stringSerializer,longSerializer, stringSerializer);         sliceQuery.setColumnFamily("StateCity");         sliceQuery.setKey("TX Austin");                 //way 1: set multiplecolumnNames         sliceQuery.setColumnNames(202L, 203L,204L);                 //way 2: use setRange         // change 'reversed' totrue to get the columns in reverse order         //sliceQuery.setRange(202L,204L, false, 5);                  QueryResult<ColumnSlice<Long,String>> result = sliceQuery.execute();         returnresult;     }

4.2.2. Sample Code runby Maven

C:\projects_learning\learning-cassandra-tutorial>mvn-e exec:java -Dexec.args="get_slice_sc"-Dexec.mainClass="com.datastax.tutorial.TutorialRunner"

The output is:

[INFO] ---exec-maven-plugin:1.1.2-Beta1:java (default-cli) @ cassandra-tutorial --- ColumnSlice([HColumn(202=30.27x097.74),HColumn(203=30.27x097.74), HColumn(204=30.32x097.73)] [INFO]------------------------------------------------------------------------ [INFO] BUILD SUCCESS

4.2.3. CLI(TODO)

TODO: Refering to CLI Syntax, Cassandra can’t getmultiple columns at one ‘get’ command?

4.3. Get multiple rows by a set of Key
4.3.1. Sample Code

public QueryResult<Rows<String,String,String>>execute() {         MultigetSliceQuery<String, String,String> multigetSlicesQuery =             HFactory.createMultigetSliceQuery(keyspace, stringSerializer,stringSerializer, stringSerializer);         multigetSlicesQuery.setColumnFamily("Npanxx");         multigetSlicesQuery.setColumnNames("city","state","lat","lng");                multigetSlicesQuery.setKeys("512202","512203","512205","512206");         QueryResult<Rows<String,String, String>> results = multigetSlicesQuery.execute();         returnresults;     }

4.3.2. Sample Code runby Maven

C:\projects_learning\learning-cassandra-tutorial>mvn-e exec:java -Dexec.args="multiget_slice"-Dexec.mainClass="com.datastax.tutorial.TutorialRunner"

The output is:
[INFO] --- exec-maven-plugin:1.2:java (default-cli) @cassandra-tutorial ---
Rows({
512205=Row(512205,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.32), HColumn(lng=097.73), HColumn(state=TX)])),
512206=Row(512206,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.32), HColumn(lng=097.73), HColumn(state=TX)])),
512203=Row(512203,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.27), HColumn(lng=097.74), HColumn(state=TX)])),
512202=Row(512202,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.27), HColumn(lng=097.74), HColumn(state=TX)]))})
[INFO]------------------------------------------------------------------------
[INFO] BUILD SUCCESS
4.3.3. CLI(TODO)

TODO: N/A?

4.4. Get Slices from a Range of Rowsby Key
4.4.1. Sample Code
GetRangeSlicesForStateCity.java

publicQueryResult<OrderedRows<String,String,String>> execute() {         RangeSlicesQuery<String, String,String> rangeSlicesQuery =             HFactory.createRangeSlicesQuery(keyspace, stringSerializer,stringSerializer, stringSerializer);         rangeSlicesQuery.setColumnFamily("Npanxx");         rangeSlicesQuery.setColumnNames("city","state","lat","lng");                rangeSlicesQuery.setKeys("512202", "512205");         rangeSlicesQuery.setRowCount(5);         QueryResult<OrderedRows<String,String, String>> results = rangeSlicesQuery.execute();         returnresults;     }

Important Note: The result actually is NOT meaningful (expectedreturn might be 512202-512205, 4 rows, but actually not) since the Key issorted by RandomPartitioner (which can be configured in/conf/cassandra.yaml, but not recommend to do so).  The result can be referred at “Sample Coderun by Maven”.
4.4.2. Sample Code runby Maven

C:\projects_learning\learning-cassandra-tutorial>mvn-e exec:java -Dexec.args="get_range_slices"-Dexec.mainClass="com.datastax.tutorial.TutorialRunner"

The output is:
[INFO] --- exec-maven-plugin:1.2:java (default-cli) @cassandra-tutorial ---
Rows({
512202=Row(512202,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.27), HColumn(lng=097.74), HColumn(state=TX)])),
512206=Row(512206,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.32), HColumn(lng=097.73), HColumn(state=TX)])),
512205=Row(512205,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.32), HColumn(lng=097.73), HColumn(state=TX)]))
})
[INFO]------------------------------------------------------------------------
[INFO] BUILD SUCCESS
4.4.3. CLI(TODO)

TODO: N/A

4.5. Get Slices from a Range of Rowsby Columns
4.5.1. Sample Code
GetSliceForAreaCodeCity.java

publicQueryResult<ColumnSlice<String,String>> execute() {         SliceQuery<String,String, String> sliceQuery =             HFactory.createSliceQuery(keyspace, stringSerializer, stringSerializer, stringSerializer);        sliceQuery.setColumnFamily("AreaCode");         sliceQuery.setKey("512");         // change the order argument to 'true' to get the last 2 columns indescending order         // gets the first 4 columns "between" Austin and Austin__204according to comparator         sliceQuery.setRange("Austin", "Austin__204", false, 5);          QueryResult<ColumnSlice<String, String>> result =sliceQuery.execute();           return result;     }

4.5.2. Sample Code runby Maven

C:\projects_learning\learning-cassandra-tutorial>mvn-e exec:java -Dexec.args="get_slice_acc"-Dexec.mainClass="com.datastax.tutorial.TutorialRunner"

The output is:
[INFO] --- exec-maven-plugin:1.2:java (default-cli) @cassandra-tutorial ---
ColumnSlice([
HColumn(Austin__202=30.27x097.74),
HColumn(Austin__203=30.27x097.74),
HColumn(Austin__204=30.32x097.73)
])
[INFO]------------------------------------------------------------------------
[INFO] BUILD SUCCESS
4.5.3. CLI

N/A

4.6. Get Slices from Indexed Columns
4.6.1. Sample Code
GetIndexedSlicesForCityState.java

public QueryResult<OrderedRows<String,String, String>> execute() {        IndexedSlicesQuery<String, String, String> indexedSlicesQuery =             HFactory.createIndexedSlicesQuery(keyspace, stringSerializer, stringSerializer, stringSerializer);        indexedSlicesQuery.setColumnFamily("Npanxx");        indexedSlicesQuery.setColumnNames("city","lat","lng");        indexedSlicesQuery.addEqualsExpression("state", "TX");        indexedSlicesQuery.addEqualsExpression("city", "Austin");        indexedSlicesQuery.addGteExpression("lat", "30.30");        QueryResult<OrderedRows<String, String, String>> result =indexedSlicesQuery.execute();                  return result;     }

4.6.2. Sample Code runby Maven
The output is:
[INFO] --- exec-maven-plugin:1.2:java (default-cli) @cassandra-tutorial ---
Rows({512204=Row(
512204,ColumnSlice([HColumn(city=Austin), HColumn(lat=30.32),HColumn(lng=097.73)])),
512206=Row(512206,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.32), HColumn(lng=097.73)])),
512205=Row(512205,ColumnSlice([HColumn(city=Austin),HColumn(lat=30.32), HColumn(lng=097.73)]))})
[INFO]------------------------------------------------------------------------
[INFO] BUILD SUCCESS
4.6.3. CLI

[default@Tutorial] get npanxx where state='TX' andcity='Austin'and lat>'30.30'; ------------------- RowKey: 512204 => (column=city, value=Austin, timestamp=1329299521508000) => (column=lat, value=30.32, timestamp=1329299521540000) => (column=lng, value=097.73,timestamp=1329299521555000) => (column=state, value=TX,timestamp=1329299521524000) ------------------- RowKey: 512206 => (column=city, value=Austin, timestamp=1329299521618000) => (column=lat, value=30.32,timestamp=1329299521633000) => (column=lng, value=097.73,timestamp=1329299522491000) => (column=state, value=TX,timestamp=1329299521618000) ------------------- RowKey: 512205 => (column=city, value=Austin, timestamp=1329299521555000) => (column=lat, value=30.32,timestamp=1329299521586000) => (column=lng, value=097.73,timestamp=1329299521602000) => (column=state, value=TX,timestamp=1329299521571000)   3 Rows Returned. Elapsed time: 16 msec(s).

 
4.7. Insertion
4.7.1. Sample Code
InsertRowsForColumnFamilies.java

public QueryResult<?> execute() {         Mutator<String>mutator = HFactory.createMutator(keyspace, stringSerializer);                 mutator.addInsertion("CA Burlingame", "StateCity", HFactory.createColumn(650L,"37.57x122.34",longSerializer,stringSerializer));         mutator.addInsertion("650", "AreaCode", HFactory.createStringColumn("Burlingame__650", "37.57x122.34"));         mutator.addInsertion("650222", "Npanxx", HFactory.createStringColumn("lat", "37.57"));         mutator.addInsertion("650222", "Npanxx", HFactory.createStringColumn("lng", "122.34"));         mutator.addInsertion("650222", "Npanxx", HFactory.createStringColumn("city", "Burlingame"));         mutator.addInsertion("650222", "Npanxx", HFactory.createStringColumn("state", "CA"));                                 MutationResult mr =mutator.execute();         return null;     }

4.7.2. Sample Code runby Maven

Omitted

4.7.3. CLI

[default@Tutorial] set StateCity['CABurlingame']['650']='37.57x122.34'; [default@Tutorial] set AreaCode[‘650'][‘Burlingame__650’]=’37.57x122.34'; [default@Tutorial] setNpanxx['650222']['lat']='37.57'; …

4.8. Deletion
4.8.1. Sample Code
InsertRowsForColumnFamilies.java

public QueryResult<?> execute() {         Mutator<String>mutator = HFactory.createMutator(keyspace, stringSerializer);                 //Mutator.addDeletion(String key, String cf, String columnName, Serializer<String>nameSerializer)         //columnName as null means to delete the whole row.         mutator.addDeletion("CA Burlingame", "StateCity", null, stringSerializer);         mutator.addDeletion("650", "AreaCode", null, stringSerializer);         mutator.addDeletion("650222", "Npanxx", null, stringSerializer);         // adding a non-existent key like the following will cause the insertionof a tombstone         // mutator.addDeletion("652", "AreaCode", null,stringSerializer);         MutationResult mr =mutator.execute();         return null;       }

4.8.2. Sample Code runby Maven

Omitted…

4.8.3. CLI

[default@Tutorial] del StateCity['CA Burlingame']; [default@Tutorial] del AreaCode['650']; [default@Tutorial] delNpanxx['650222'];

Important Note: Whatever you use, either java code or CLI, thedeletion event will still leave the DeletedColumn row key there marked as Tombstone(hehe, 墓碑, a really good naming) which can be retrieved backby command of ‘list’ like this.

[default@Tutorial]list StateCity; Usingdefault limit of 100 ------------------- RowKey: CA Burlingame ------------------- RowKey: TXAustin =>(column=202, value=30.27x097.74, timestamp=1329297768323000) =>(column=203, value=30.27x097.74, timestamp=1329297768338000) =>(column=204, value=30.32x097.73, timestamp=1329297768354000) =>(column=205, value=30.32x097.73, timestamp=1329297768370000) =>(column=206, value=30.32x097.73, timestamp=1329297768385000) 2 Rows Returned. Elapsedtime: 16 msec(s).

Asyou see, two rows returned! Even the row of ‘CA Burlingame’ has been deleted.
Evenworse, if the deletion of non-existing key will cause an issue called ‘insertionof a tombstone’ which means it will add one more row in the Column Family!!!
Fortrunately,the command of ‘get’ won’t retrieve it back any more.

[default@Tutorial] get StateCity['CA Burlingame']; Returned 0 results. Elapsed time: 0 msec(s).

 
Godeeper? Please read on.
Whenwill Cassandra remove these tombstones? As I know, two ways:
1. Wait until gc_grace_seconds istimeout (Not verified yet)
Thegc_grace_seconds is set per CF and can be updated without a restart.
Howto get gc_grace_seconds? Simply use CLI:

[default@Tutorial] show schema; … create column family StateCity   withcolumn_type = 'Standard'   andcomparator = 'LongType'   anddefault_validation_class = 'UTF8Type'   andkey_validation_class = 'UTF8Type'   androws_cached = 0.0   androw_cache_save_period = 0   androw_cache_keys_to_save = 2147483647   andkeys_cached = 200000.0   andkey_cache_save_period = 14400   andread_repair_chance = 1.0   and gc_grace =864000   // 10 days, OMG   andmin_compaction_threshold = 4   andmax_compaction_threshold = 32   andreplicate_on_write = true   and row_cache_provider= 'ConcurrentLinkedHashCacheProvider' and compaction_strategy ='org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'; …

 
2. The Compaction event (underinvestigation but no luck yet)
TheCompaction will be triggered automatically.
Buthow to trigger compaction manually? Use nodetool as well.

C:\java\apache-cassandra-1.0.7\bin>nodetool -hlocalhost flush Tutorial Starting NodeTool C:\java\apache-cassandra-1.0.7\bin>nodetool -hlocalhost compact Tutorial Starting NodeTool

Thenwe can see some logging messages in the Cassandra console.
Butas I found, the tombstones are still here. (WHY???)

C:\java\apache-cassandra-1.0.7\bin>sstable2json..\runtime\data\Tutorial\StateCity-hc-9-Data.db { "4341204275726c696e67616d65":[["650","37.57x122.34",1329316454906000]], "54582041757374696e":[["202","30.27x097.74",1329297768323000],["203","30.27x097.74",1329297768338000],["204","30.32x097.73",1329297768354000],["205","30.32x097.73",1329297768370000],["206","30.32x097.73",1329297768385000]], "616263": [] }

Andstill appears in the list command. (KAO, 阴魂不散? Big why???)

[default@Tutorial] list statecity; Using default limit of 100 ------------------- RowKey: CA Burlingame ------------------- RowKey: TX Austin => (column=202, value=30.27x097.74,timestamp=1329297768323000) => (column=203, value=30.27x097.74,timestamp=1329297768338000) => (column=204, value=30.32x097.73,timestamp=1329297768354000) => (column=205, value=30.32x097.73,timestamp=1329297768370000) => (column=206, value=30.32x097.73,timestamp=1329297768385000) ------------------- RowKey: abc   3 Rows Returned. Elapsed time: 31 msec(s).

 
 
在这儿咱发几句牢骚：
1. 可能是学习深度还不足的原因，感觉CLI比较弱，适合初始化建模DDL和简单的数据分析；
2. Tombstone的清理问题还没有最终得到验证，暂时挂起，权当悬案先，以后有答案了再补充、更正