{"id":20298,"date":"2013-05-10T12:49:09","date_gmt":"2013-05-10T07:19:09","guid":{"rendered":"http:\/\/vskills.in\/certification\/tutorial\/?p=20298"},"modified":"2024-04-12T14:16:40","modified_gmt":"2024-04-12T08:46:40","slug":"deletion-and-programmatic-definition","status":"publish","type":"page","link":"https:\/\/www.vskills.in\/certification\/tutorial\/deletion-and-programmatic-definition\/","title":{"rendered":"Deletion and programmatic definition"},"content":{"rendered":"

Certify and Increase Opportunity.<\/span>
\nBe <\/span>
\nGovt. Certified Apache Cassandra Professional
\n<\/span><\/a><\/p>\n

Deletion and programmatic definition<\/strong><\/h3>\n

Data written to Cassandra gets persisted to SSTables. Since SSTables are immutable, the data can’t actually be removed when you perform a delete, instead, a marker (also called a “tombstone”) is written to indicate the value’s new status. Never fear though, on the first compaction that occurs between the data and the tombstone, the data will be expunged completely and the corresponding disk space recovered.<\/p>\n

DELETE Usage<\/span><\/p>\n

DELETE [<column_name> [, …]]\nFROM <column_family>
\n[USING CONSISTENCY <consistency_level> [AND TIMESTAMP <integer>]]\nWHERE <row_specification>;<\/p>\n

<row_specification> is:<\/p>\n

KEY | <key_alias> = <key_value>
\nKEY | <key_alias> IN (<key_value> [,…])<\/p>\n

Description<\/span>
\nA DELETE statement removes one or more columns from one or more rows in the named column family.<\/p>\n

Specifying Columns<\/span>
\nAfter the DELETE keyword, optionally list column names, separated by commas.<\/p>\n

DELETE col1, col2, col3 FROM Planeteers USING CONSISTENCY ONE WHERE KEY = ‘Captain’;<\/p>\n

When no column names are specified, the entire row(s) specified in the WHERE clause are deleted.<\/p>\n

DELETE FROM MastersOfTheUniverse WHERE KEY IN (‘Man-At-Arms’, ‘Teela’);<\/p>\n

Specifying the Column Family<\/span>
\nThe column family name follows the list of column names and the keyword FROM.<\/p>\n

Specifying Options<\/p>\n

You can specify these options:<\/p>\n

Consistency level
\nTimestamp (current time)<\/p>\n

When a column is deleted, it is not removed from disk immediately. The deleted column is marked with a tombstone and then removed after the configured grace period has expired. The optional timestamp defines the new tombstone record. See About Deletes for more information about how Cassandra handles deleted columns and rows.<\/p>\n

Specifying Rows<\/span><\/p>\n

The WHERE clause specifies which row or rows to delete from the column family. This form allows the specification of a single keyname using the KEY keyword (or key alias) and the = operator.<\/p>\n

DELETE col1 FROM SomeColumnFamily WHERE KEY = ‘some_key_value’;<\/p>\n

This form provides a list of key names using the IN notation and a parenthetical list of comma-delimited keyname terms.<\/p>\n

DELETE col1 FROM SomeColumnFamily WHERE keyalias IN (key1, key2);<\/p>\n

Example<\/p>\n

DELETE email, phone
\nFROM users
\nUSING CONSISTENCY QUORUM AND TIMESTAMP 1318452291034
\nWHERE user_name = ‘jsmith’;
\nDELETE phone FROM users WHERE KEY IN (‘jdoe’, ‘jsmith’);<\/p>\n

Programmatic Column Addition<\/span><\/p>\n

cluster.addColumnFamily(ColumnFamilyDefinition cfdef); \/\/ where the
\n‘cluster’ is derived from new ThriftCluster(“Cluster1”,
\ncassandraHostConfigurator);<\/p>\n

Another example for programmatic addition is –<\/p>\n

The unit test for Cluster has some examples for creating keyspaces and\ncolumn families dynamically:\nhttps:\/\/github.com\/rantav\/hector\/blob\/master\/core\/src\/test\/java\/me\/prettyprint\/cassandra\/service\/CassandraClusterTest.java#L88-179<\/a><\/pre>\n
\n
Apply for Apache Cassandra Certification Now!!<\/h3>\n
http:\/\/www.vskills.in\/certification\/Certified-Apache-Cassandra-Professional<\/a><\/p>\n
Go To Tutorial- Certified Apache Cassandra Professional Tutorial<\/strong><\/a><\/h5>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
Certify and Increase Opportunity. Be Govt. Certified Apache Cassandra Professional Deletion and programmatic definition Data written to Cassandra gets persisted to SSTables. Since SSTables are immutable, the data can’t actually be removed when you perform a delete, instead, a marker (also called a “tombstone”) is written to indicate the value’s new status. Never fear though,…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"categories":[63],"tags":[],"class_list":["post-20298","page","type-page","status-publish","hentry","category-apache-cassandra"],"acf":[],"yoast_head":"\nDeletion and programmatic definition - Tutorial<\/title>\n<meta name=\"description\" content=\"Deletion and programmatic definition. 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