CODEWITHSUNDEEP
hadoophbase
Brainchild
Brainchild

Reputation: 1874

How consistency works in HBase

From the CAP, I read HBase supports consistency and partition tolerance. I would like to know how consistency is achieved in HBase. Any locks are applied?

I checked online didn't find good material on this. Could any body provide any blogs/articles on this topic.

Upvotes: 5

Views: 6450

Answers (2)

Mehdi LAMRANI
Mehdi LAMRANI

Reputation: 11597

The answer provided by Evgeny is correct but very incomplete.
Contrary to what you wrote, there are many resources and blog articles and good material concerning this specific aspect. The tricky part is to aggregate separate information and make your own synthesis. Consistency is dealt with in HBase at many levels, and you need to understand those different levels to get a good global understanding of how it is managed.
HBase it a complex beast, give it time.

You can start by reading about Read/Write Path, Timeline-consistent High Available Reads, and Region Replication.

https://hbase.apache.org/book.html#arch.timelineconsistent.reads

https://mapr.com/blog/in-depth-look-hbase-architecture/

Upvotes: 3

Evgeny Benediktov
Evgeny Benediktov

Reputation: 1399

Access to row data is atomic and includes any number of columns being read or written to. There is no further guarantee or transactional feature that spans multiple rows or across tables. The atomic access is a factor to this architecture being strictly consistent, as each concurrent reader and writer can make safe assumptions about the state of a row.

When data is updated it is first written to a commit log, called a write-ahead log (WAL) in HBase, and then stored in the (sorted by RowId) in-memory memstore. Once the data in memory has exceeded a given maximum value, it is flushed as an HFile to disk. After the flush, the commit logs can be discarded up to the last unflushed modification.

Thus a lock is needed only to protect the row in RAM.

Upvotes: 12

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