Cassandra data compression

  • Does Cassandra compress data?

    Cassandra offers operators the ability to configure compression on a per-table basis.
    Compression reduces the size of data on disk by compressing the SSTable in user-configurable compression chunk_length_in_kb ..

  • How do I turn off compression in Cassandra?

    Once enabled, compression can be disabled with ALTER TABLE setting enabled to false : ALTER TABLE keyspace. table WITH compression = {'enabled':'false'};.

  • How does Cassandra store data?

    When a write occurs, Cassandra stores the data in a memory structure called memtable, and to provide configurable durability, it also appends writes to the commit log on disk.
    The commit log receives every write made to a Cassandra node, and these durable writes survive permanently even if power fails on a node..

  • How does compaction work in Cassandra?

    Cassandra triggers minor compaction automatically.
    In major compaction, a user executes a Cassandra compaction across the node.
    In other words, each of the SSTables are compacted on the node.
    Finally, in a user defined compaction, the user triggers the Cassandra compaction across a specific set of SSTables..

  • What are the limitations of Cassandra database?

    Here are Cassandra's downsides: It doesn't support ACID and relational data properties.
    Because it handles large amounts of data and many requests, transactions slow down, meaning you get latency issues.
    Data is modeled around queries and not structure, resulting in the same information stored multiple times..

  • What is the recommended disk size for Cassandra?

    Maximum recommended capacity for Cassandra 1.2 and later is 3 to .

    1. TB per node for uncompressed data
      2. ." With our current compression levels of around 17%, this translates to no more than 500-85.
    2. G of compressed storage per node

  • By default, the chunk size of compressed data is 6.
    1. Kb.
      2. This means that the database needs to read the entire amount to extract the necessary data and puts an additional load on the disk system when not needed.
  • Cassandra's hard limit is 2 billion cells per partition, but you'll likely run into performance issues before reaching that limit.
    The number of values (or cells) in the partition (Nv) is equal to the number of static columns (Ns) plus the product of the number of rows (Nr) and the number of of values per row.
  • Once enabled, compression can be disabled with ALTER TABLE setting enabled to false : ALTER TABLE keyspace. table WITH compression = {'enabled':'false'};
Because random-access read from the data file is important, Apache Cassandra implements chunked compression: The uncompressed file is divided into chunks of a configurable fixed size (usually 64 KB), and each of these chunks is compressed separately and written to the compressed data file, followed by a 4-byte checksum
Compression maximizes the storage capacity of Cassandra nodes by reducing the volume of data on disk and disk I/O, particularly for read-dominated workloads. Compression is best suited for tables that have many rows and each row has the same columns, or at least as many columns, as other rows.

Compression Benefits

Besides data size, compression typically improves both read and write performance.
Cassandra is able to quickly find the location of rows in the SSTable index, and only decompresses the relevant row chunks.
This means compression improves read performance not just by allowing a larger data set to fit in memory, but it also benefits workloads where .

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Conclusion

Compression in Cassandra 1.0 is an easy way to reduce storage volume requirements while increasing performance.
Compression can be easily added to existing ColumnFamilies after an upgrade, and the implementation allows power users to tweak chunk sizes for maximum benefit.

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Configuring Compression on A Columnfamily

When you create or update a column family, you can choose to make it a compressed column family by specifying the following storage properties: 1. compression_options: this is a container property for setting compression options on a column family.
The compression_options property contains the following options: 1.1. sstable_compression: specifies .

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Does Cassandra support serializability?

As of version 3.0, Cassandra does not support serializability, or isolation (the “I” in ACID.) Serializability is important in applications where strong data consistency and transactions are required.

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How does a Cassandra cluster work?

Each node in a Cassandra cluster also maintains a sequential commit log of write activity on disk to ensure data integrity.
These writes are indexed and written to an in-memory structure called a memtable.

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How does Cassandra write data?

In Cassandra, while writing data, writes are written to any node in the cluster (coordinator). when any user will insert data, it means they write the data first to commit log then to memtable.
When any user will write the data, every write will include:

  1. a timestamp
,

What is the Cassandra storage engine?

At its core, Cassandra uses a Log Structured Merge (LSM) storage engine.
The following are the key elements of the Cassandra storage engine… Each node in a Cassandra cluster also maintains a sequential commit log of write activity on disk to ensure data integrity.

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When to Use Compression

Compression is best suited for ColumnFamilies where there are many rows, with each row having the same columns, or at least many columns in common.
For example, a ColumnFamily containing user data such as username, email, etc., would be a good candidate for compression.
The more similar the data across rows, the greater the compression ratio will b.

What is compression metadata in Cassandra?

Along side each compressed SSTable is compression metadata

The compression files have names like na-9-big-CompressionInfo

db

The compression metadata is stored in memory, off the Cassandra heap

The size of the offheap usage is directly proportional to the amount of chunks used

More chunks = more space used

What is the Cassandra data model?

The Cassandra Data Model is a page in the Apache Cassandra 1

0 Documentation that describes some key differences between Cassandra and relational databases

These include: There are no foreign keys in Cassandra and there is no "joining" in Cassandra

Denormalization is not a shameful thing in Cassandra and is actually welcomed to a certain degree

What is the Cassandra storage engine?

At its core, Cassandra uses a Log Structured Merge (LSM) storage engine

The following are the key elements of the Cassandra storage engine… Each node in a Cassandra cluster also maintains a sequential commit log of write activity on disk to ensure data integrity

Compression can be an effective way to reduce the size of your data, which in turn can improve read latency. Cassandra offers several compression algorithms, including LZ4 and Snappy. These algorithms can significantly reduce the amount of data that needs to be read from disk, resulting in faster read times.
Cassandra data compression
Cassandra data compression

Free and open-source database management system

Cassandra is a free and open-source, distributed, wide-column store, NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure.
Cassandra offers support for clusters spanning multiple datacenters, with asynchronous masterless replication allowing low latency operations for all clients.
Cassandra was designed to implement a combination of Amazon's Dynamo distributed storage and replication techniques combined with Google's Bigtable data and storage engine model.

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