How Cassandra Reads the data?
To Satisfy read/write request, it must achieve consistency level (whatever we define, either CL = 1, 2 or Quorum. To know more, please check consistency level).
To complete the read request, Cassandra combine the request set of active MemTable and SSTables.
Cassandra fetch data from multiple stages to discover where the data is stored and which one is latest.
Cassandra fetch the data from below given stages : –
- Check the data from MemTable
- Check the row cache if enabled
- Check the Bloom Filter
- Check the Partition key cache if enabled
- It directly goes to Compression Offset if found in partition key cache, to check where the data partion is in SSTables, if not found in partition key cache then it will go to partition key index.
- If it checks in Partition Summary then it check Partition index.
- It check in Compression Offset to locate the data on the disk.
- Fetch the data from SSTable on the disk.
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