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ashok.dcosta_187920 avatar image
ashok.dcosta_187920 asked ·

Which data structures are supported by SSTables?

Which 3 data structures is supported by SS table from the below ?

- Bloom Filter

- Partition table

- Parititon Index

- Partition Summary

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Erick Ramirez avatar image
Erick Ramirez answered ·

The Bloom filter is a data structure that helps determine the probability that an SSTable contains partition data. Serialised bloom filter of the partition keys are stored in the *-Filter.db component of the SSTables which get read into off-heap memory.

The partition index contains the index of partition keys in an SSTable and their corresponding offset or pointers to their position in the SSTable. The partition index is stored on disk in the *-Index.db component of the SSTables and is cached in off-heap memory as the partition key cache.

The partition summary is a sample (subset) of the partition index used to optimise reads. The partition summary is stored on disk in the *-Summary.db component of the SSTables which get read into off-heap memory.

"Partition table" is not a SSTable data structure.

These structures are discussed in more detail in How data is read in Cassandra. Cheers!

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saravanan.chinnachamy_185977 avatar image
saravanan.chinnachamy_185977 answered ·

@ashok.dcosta_187920 Cassandra processes data at several stages on the read path to discover where the data is stored, starting with the data in the memtable and finishing with SSTables:

Some of the stages checked are memtable,Bloom filter,partition key ,partition summary.

For more information please refer to Cassandra Read Path

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THis is a interview question i was asked .Does this mean the data structures supported by SS table are Bloom Filter, Partition index and partition summary ? Are these the correct answers ?

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A friendly note to let you know that I've converted your post to a comment since it's not an "answer". Cheers!

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