I am new to Cassandra & I am using the Hector Java Client for writing/reading from it.
I've the following code to insert values -
Mutator<String> mutator = HFactory.createMutator(keyspaceOperator, StringSerializer.get());
mutator.insert("jsmith", stdColumnDefinition, HFactory.createStringColumn("first", "John"));
Now, when I get the values back via the Hector client - it works cleanly -
columnQuery.setColumnFamily(stdColumnDefinition).setKey("jsmith").setName("first");
QueryResult<HColumn<String, String>> result = columnQuery.execute();
However, when I try to get the values from the command line cassandra client, I get the data in bytes, rather than human readable String format. Is there a way for me to fix this so that I can use the cassandra client to spit out Strings -
here is the sample output
[default#keyspaceUno] list StandardUno ;
Using default limit of 100
RowKey: 6a736d697468
=> (column=6669727374, value=4a6f686e, timestamp=1317183324576000)
=> (column=6c617374, value=536d697468, timestamp=1317183324606000)
1 Row Returned.
Thanks.
You can either modify the schema so that Cassandra interprets the column as a string by default, or you can tell the CLI how to interpret the data, either on a one-shot basis, or for the rest of the session, using the "assume" command.
See http://www.datastax.com/docs/0.8/dml/using_cli#reading-rows-and-columns for examples.
Related
The DataStax documentation says that to page through all data, the following CQL query is useful:
SELECT * FROM test WHERE token(k) > token(42);
Is it possible to build this query using the QueryBuilder? It provides a token method, but that seems to work only on column names, not on values.
Ideally, the value (in the example: 42) is of type Object, just like in the eq/gte/lte functions.
Try using automatic paging with the .fetchSize method. It uses token under the hood:
Automatic paging is introduced Cassandra 2.0. Automatic paging allows the developer to iterate on an entire ResultSet without having to care about its size: some extra rows are fetched as the client code iterate over the results while the old ones are dropped. The amount of rows that must be retrieved can be parameterized at query time. In the Java Driver this will looks like:
Statement stmt = new SimpleStatement("SELECT * FROM images");
stmt.setFetchSize(100);
ResultSet rs = session.execute(stmt);
Source: http://www.datastax.com/dev/blog/client-side-improvements-in-cassandra-2-0
QueryBuilder.fcall("token", value) ;
can solve the problem！
I have table created using map in cassandra, Now i am trying to read the table from node.js and it returns object for the map, can i get the item count in a map and loop through it to get the items in the map?
table script
create table workingteam (teamid bigint primary key, status map)
You did not post a lot of details. First you will need to study the object Cassandra sends you. Good way to start would be to convert it to the JSON format and dump to the output through log.
console.log("Cassandra sent: %j", object);
I'm guessing in this object you will find attributes like connection parameters, host, client etc, but also something iterative that will contain keys and values.
I am very new to Cassandra and this time still I have not done my part on reading much about the architecture. I have a simple question for which I am not getting an answer for.
This is a sample data when I do a list abcColumnFamily:
RowKey:Message_1
=> (column=word, value=Message_1, timestamp=1373976339934001)
RowKey:Message_2
=> (column=word, value=Message_2, timestamp=1373976339934001)
How can I search for the Rowkey having say Message_1
In SQL world: Select * from Table where Rowkey = 'Message_1' (= OR like). I want to simply search on full string.
My intention is to just check whether a particular data of my interest is there in a rowkey or not.
For CQL try:
select * from abcColumnFamily where KEY = 'Message_1'
If You want to query that data using CLI try the following:
assume abcColumnFamily keys as utf8;
get abcColumnFamily['Message_1'];
I am using Astyanax client to read data from Cassandra column families. My requirement is to query on a secondary index column of a column family through astyanax. I was able to find a few examples from the astyanax website to read data from Cassandra using an expression on an index column. I used the examples to write my own code:
OperationResult<Rows<String, String>> result = null;
IndexQuery<String, String> query = keyspace.prepareQuery("ColumnFamilyName").searchWithIndex().setRowLimit(100).autoPaginateRows(true).addExpression().whereColumn("ColumnNameWhichHasSecondaryIndex").equals().value("value");
result = query.execute();
for(Row<String, String> row : result.getResult()) {
...
}
This is the issue I am facing while running this code is it is only returning me 100 rows, while the column family has a few thousand rows that satisfy the query criteria.
I am not able to find the right API/pattern to address my issue. Could some one please guide me on this issue please?
Astanax Version: 1.56.24
Apache Cassandra Version: 1.1.8
Jdk Version: 1.7
Platform: Rhel 5.4 32bit
setRowLimit(100) means every time you execute the query, it return at most 100 items.
So if you have more than 100 items, you should execute query again and again to get
all the result under the setting autoPaginateRows(true)
Increase your row limit:
.setRowLimit(100)
trying to write a query which will paginate through all rows in a column family using astyanax client and RowSliceQuery.
keyspace.prepareQuery(COLUMN_FAMILY).getKeyRange(null, null, null, null, 100);
Done this successfully using hector where 1st call is done with null start and end keys. After retrieving 1st page I use last key from the result to make query for second page and etc. This is code for 1st page using hector.
HFactory.createRangeSlicesQuery(keyspace,
LongSerializer.get(), new CompositeSerializer(),
BytesArraySerializer.get())
.setColumnFamily(COLUMN_FAMILY)
.setRange(null, null, false, 100).setRowCount(100);
Now when I am trying to do this with astyanax I am getting errors about null and non-null keys and tokens. Not sure what tokens do in this query. Also I am able to use allRows(), but would like to do this using key range query as it gives me more flexibility.
Does anybody have an example of key range query using astyanax? I cannot find an example neither in "getting started" documentation or anywhere else on the net.
Thanks!
Anton
What you are referring to is the getRowRange method:
keyspace.prepareQuery(CF_STANDARD1)
.getRowRange(startKey, endKey, startToken, endToken, count)
Note however that this works only when the ByteOrderedPartitioner is used. Since by default Cassandra uses the Murmur3Partitioner, this will usually not work. Using an index to do this instead is recommended. Astyanax also provides the reverse index search recipe which takes advantage of a second column family which stores your keys as columns to allow efficient range searches on the original data.
Check this sample code. I hope this code will help you in doing the paging.
IndexQuery<String, String> query = keyspace
.prepareQuery(CF_STANDARD1).searchWithIndex()
.setRowLimit(10).autoPaginateRows(true).addExpression()
.whereColumn("Index2").equals().value(42);
Best,