Apache Cassandra Learning Step by Step (3): Samples ABC
====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:
--- exec-maven-plugin:1.1.2-Beta1:java(default-cli) @ cassandra-tutorial ---
HColumn(city=Austin)
------------------------------------------------------------------------
BUILD SUCCESS
4.1.3. CLI
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:
---exec-maven-plugin:1.1.2-Beta1:java (default-cli) @ cassandra-tutorial ---
ColumnSlice(
------------------------------------------------------------------------
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:
--- exec-maven-plugin:1.2:java (default-cli) @cassandra-tutorial ---
Rows({
512205=Row(512205,ColumnSlice()),
512206=Row(512206,ColumnSlice()),
512203=Row(512203,ColumnSlice()),
512202=Row(512202,ColumnSlice())})
------------------------------------------------------------------------
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:
--- exec-maven-plugin:1.2:java (default-cli) @cassandra-tutorial ---
Rows({
512202=Row(512202,ColumnSlice()),
512206=Row(512206,ColumnSlice()),
512205=Row(512205,ColumnSlice())
})
------------------------------------------------------------------------
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:
--- 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)
])
------------------------------------------------------------------------
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:
--- exec-maven-plugin:1.2:java (default-cli) @cassandra-tutorial ---
Rows({512204=Row(
512204,ColumnSlice()),
512206=Row(512206,ColumnSlice()),
512205=Row(512205,ColumnSlice())})
------------------------------------------------------------------------
BUILD SUCCESS
4.6.3. CLI
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
set StateCity['CABurlingame']['650']='37.57x122.34';
set AreaCode[‘650'][‘Burlingame__650’]=’37.57x122.34';
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
del StateCity['CA Burlingame'];
del AreaCode['650'];
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.
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.
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:
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???)
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
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