hbase-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "cuijianwei (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-10999) Cross-row Transaction : Implement Percolator Algorithm on HBase
Date Wed, 16 Apr 2014 06:56:14 GMT
cuijianwei created HBASE-10999:

             Summary: Cross-row Transaction : Implement Percolator Algorithm on HBase
                 Key: HBASE-10999
                 URL: https://issues.apache.org/jira/browse/HBASE-10999
             Project: HBase
          Issue Type: New Feature
          Components: Transactions/MVCC
    Affects Versions: 0.94.18
            Reporter: cuijianwei

Cross-row transaction is a desired function for database. It is not easy to keep ACID characteristics
of cross-row transactions in distribute databases such as HBase, because data of cross-transaction
might locate in different machines. In the paper http://research.google.com/pubs/pub36726.html,
google presents an algorithm(named percolator) to implement cross-row transactions on BigTable.
After analyzing the algorithm, we found percolator might also be a choice to provide cross-row
transaction on HBase. The reasons includes:
1. Percolator could keep the ACID of cross-row transaction as described in google's paper.
Percolator depends on a Global Incremental Timestamp Service to define the order of transactions,
this is important to keep ACID of transaction.
2. Percolator algorithm could be totally implemented in client-side. This means we do not
need to change the logic of server side. Users could easily include percolator in their client
and adopt percolator APIs only when they want cross-row transaction.
3. Percolator is a general algorithm which could be implemented based on databases providing
single-row transaction. Therefore, it is feasible to implement percolator on HBase.
In last few months, we have implemented percolator on HBase, did correctness validation, performance
test and finally successfully applied this algorithm in our production environment. Our works
1. percolator algorithm implementation on HBase. The current implementations includes:
    a). a Transaction module to provides put/delete/get/scan interfaces to do cross-row/cross-table
    b). a Global Incremental Timestamp Server to provide globally monotonically increasing
timestamp for transaction.
    c). a LockCleaner module to resolve conflict when concurrent transactions mutate the same
    d). an internal module to implement prewrite/commit/get/scan logic of percolator.
   Although percolator logic could be totally implemented in client-side, we use coprocessor
framework of HBase in our implementation. This is because coprocessor could provide percolator-specific
Rpc interfaces such as prewrite/commit to reduce Rpc rounds and improve efficiency. Another
reason to use coprocessor is that we want to decouple percolator's code from HBase so that
users will get clean HBase code if they don't need cross-row transactions. In future, we will
also explore the concurrent running characteristic of coprocessor to do cross-row mutations
more efficiently.
2. an AccountTransfer simulation program to validate the correctness of implementation. This
program will distribute initial values in different tables, rows and columns in HBase. Each
column represents an account. Then, configured client threads will be concurrently started
to read out a number of account values from different tables and rows by percolator's get;
after this, clients will randomly transfer values among these accounts while keeping the sum
unchanged, which simulates concurrent cross-table/cross-row transactions. To check the correctness
of transactions, a checker thread will periodically scan account values from all columns,
make sure the current total value is the same as the initial total value. We run this validation
program while developing, this help us correct errors of implementation.
3. performance evaluation under various test situations. We compared percolator's APIs with
HBase's with different data size and client thread count for single-column transaction which
represents the worst performance case for percolator. We get the performance comparison result
as (below):
    a) For read, the performance of percolator is 90% of HBase;
    b) For write, the performance of percolator is 23%  of HBase.
The drop derives from the overhead of percolator logic, the performance test result is similar
as the result reported by google's paper.
4. Performance improvement. The write performance of percolator decreases more compared with
HBase. This is because percolator's write needs to read data out to check write conflict and
needs two Rpcs which do prewriting and commiting respectively. We are investigating ways to
improve the write performance.
We are glad to share current percolator implementation and hope this could provide a choice
for users who want cross-row transactions because it does not need to change the code and
logic of origin HBase. Comments and discussions are welcomed.

This message was sent by Atlassian JIRA

View raw message