Cassandra primary key (a unique identifier for a row) is made up of two parts - 1) one or more partitioning columns and 2) zero or more clustering columns. To search a table without any indexes, all partitioning columns must be provided to avoid error message: Cannot execute this query as it might involve data filtering … Continue reading Cassandra Primary Key = ((Partitioning Key), Clustering Key): A simple explanation
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Cassandra is a multi-node, peer-to-peer cluster/distributed system that distributes/stores data across all nodes in the cluster. Every table in Cassandra is physically stored in multiple SSTable files spread across one or multiple nodes. Rows are spread around the cluster based on a hash of the partition key, which is the first part of the primary key. … Continue reading How and when to index data in Cassandra for fast and efficient retrieval? – A simple explanation
Every time a record is inserted into Cassandra - it follows the write-path as per the diagram above. First, the record is written to a commit log (on disk). All records irrespective of schema tables are written to the commit log. The commit log enables recovery of memtable in case of hardware failure. Second, the … Continue reading How does Cassandra store data? – A simple explanation
Pattern #3: Get rid of all NOT operators from sql where clauses. For example, consider a typical SQL query to find all employees who have NOT completed a mandatory information security training: select ee1.* from employee ee1 where NOT exists ( select ‘true’ from employee_training et1 where et1.employeeID = ee1.employeeID and … Continue reading Migrating SQL applications to Cassandra – Pattern #3
Pattern #2: Get rid of all EXISTS and IN from sql where clauses. For example, consider a typical SQL query to find all employees who have completed a mandatory information security training: select ee1.* from employee ee1 where exists ( select 'true' from employee_training et1 where et1.employeeID = ee1.employeeID and … Continue reading Migrating SQL applications to Cassandra – Pattern #2
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