How know what column table currently holds

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Topic: Apache Cassandra -- Access via CQL

EricJ
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posted on: 09/30/2015 01:43:53 AM

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Apache Cassandra -- Access via CQL

You can start CQL console by entering:

C:\..\bin> cqlsh

If you have customized your Cassandra by:

 rpc_address: 10.11.12.13

you should use the following command:

C:\..\bin> cqlsh 10.11.12.13:9042

C:\..\bin> cqlsh 10.11.12.13

Trouble Shooting:

You may get error while executing CQLSH “can’t detect python version cqlsh”
The error indicating that, Python is not installed in your machine.
Steps to follow:

1) Download & install Python 2.7.x;

2) Add "Path" environment variable for Python directory;

3) Execute command “setup.py install” under “C:\apache-cassandra-2.2.1\pylib” to install python.

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EricJ
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posted on: 09/30/2015 01:50:04 AM

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CQL by Example

Step 1. Create a new keyspace called 'playlist'

cqlsh> create KEYSPACE playlist WITH replication 
       = {'class':'SimpleStrategy', 'replication_factor': 1 };

Step 2. Use a keyspace

cqlsh> use playlist;

Step 3. Create column families or tables

cqlsh:playlist> create table artists_by_first_letter (
       first_letter text, 
       artist text, 
       primary key (first_letter, artist));

cqlsh:playlist> create table track_by_artist (
       track text, 
       artist text, 
       track_id UUID, 
       track_length_in_seconds int, 
       genre text,music_file text, 
       primary key (artist, track, track_id));

cqlsh:playlist> create table track_by_genre (
       track text, artist text, 
       track_id UUID, 
       track_length_in_seconds int, 
       genre text,
       music_file text, 
       primary key (genre, artist, track, track_id));

Step 4. Populate the tables with data from files

cqlsh:playlist> copy artists_by_first_letter (first_letter, artist) 
     FROM 'scripts/artists.csv' WITH DELIMITER = '|';

cqlsh:playlist> copy track_by_artist (track_id, genre, artist, track, 
        track_length_in_seconds, music_file) 
     FROM 'scripts/songs.csv' 
     WITH DELIMITER = '|'  AND HEADER=true;

cqlsh:playlist> copy track_by_genre (track_id, genre, artist, track, 
        track_length_in_seconds, music_file) 
     FROM 'scripts/songs.csv' 
     WITH DELIMITER = '|'  AND HEADER=true;

Step 5. Export the tables to file

cqlsh:playlist> copy artists_by_first_letter (first_letter, artist) 
     TO 'scripts/artists_out.csv'
     WITH DELIMITER = '|' AND HEADER=true;

Step 6. Check table content

cqlsh:playlist> select * from artists_by_first_letter;

Step 7. Quit cqlsh

exit;

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EricJ
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posted on: 09/30/2015 01:53:03 AM

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How do I know what 'keyspace' the node currently hosts?

cqlsh> select * from system.schema_keyspaces;

 keyspace_name      | durable_writes | strategy_class  | strategy_options
--------------------+----------------+---------------------------------------------
        system_auth |           True | SimpleStrategy | {"replication_factor":"1"}
           playlist |           True | SimpleStrategy | {"replication_factor":"1"}
 system_distributed |           True | SimpleStrategy | {"replication_factor":"3"}
             system |           True | LocalStrategy  |                       {}
      system_traces |           True | SimpleStrategy | {"replication_factor":"2"}
(5 rows)

Here, the keyspace 'playlist' is created by user, others are system's.

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EricJ
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posted on: 09/30/2015 01:54:06 AM

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How do I know what 'table' the keyspace currently holds?

cqlsh> desc playlist;

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EricJ
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posted on: 09/30/2015 01:54:54 AM

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How do I know what 'column' the table currently holds?

cqlsh> desc playlist.artists_by_first_letter;

CREATE TABLE playlist.artists_by_first_letter (
    first_letter text,
    artist text,
    PRIMARY KEY (first_letter, artist)
) WITH CLUSTERING ORDER BY (artist ASC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = '{"keys":"ALL", "rows_per_partition":"NONE"}'
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCom
pactionStrategy'}
    AND compression = {'sstable_compression': 'org.apache.cassandra.io.compress.
LZ4Compressor'}
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99.0PERCENTILE';

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EricJ
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posted on: 09/30/2015 01:59:41 AM

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References

1. http://docs.datastax.com/en/playlist/doc/java/playlistPreface.html

2. http://www.devjavasource.com/cassandra/apache-cassandra-quick-start/

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