How does Cassandra retrieve data from SStable and merage it to memetable? Will these data be flushed again?

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  1. When I request a row with whole primary key, will Cassandra fetch all rows of that partition from SSTable and merge them into memetable, then filter that requested row? or it can find that row with clustering keys and only retrieve one row to memetable?

  2. How does SSTable store data(row by row or column by column, why some SSTables can only contain one column)? if I only request one column, could Cassandra find the location of that particular column and only return that column?

  3. How does Cassandra deal with data that retrieved from SSTable when flush memetable to SSTable, will that data be write to a new SSTable again?

Thanks a lot for any answers.

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cassandra

1 Answers

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You should take a look at datastaxacademy.com, specifically the course "DS201: DataStax Enterprise Foundations of Apache Cassandra™". The topics that you are asking for are "Read Path" and "Write path".