Jianwei Cui created HBASE-15340:
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Summary: Partial row result of scan may return data violates the
row-level transaction
Key: HBASE-15340
URL: https://issues.apache.org/jira/browse/HBASE-15340
Project: HBase
Issue Type: Bug
Components: Scanners, Transactions/MVCC
Affects Versions: 2.0.0
Reporter: Jianwei Cui
There are cases the region sever will return partial row result, such as the
client set batch for scan or configured size limit reached. In these
situations, the client may return data that violates the row-level transaction
to the application. The following steps show the problem:
{code}
// assume there is a test table 'test_table' with one family 'F' and one region
'region'.
// meanwhile there are two region servers 'rsA' and 'rsB'.
1. Let 'region' firstly located in 'rsA' and put one row with two columns 'c1'
and 'c2' as:
> put 'test_table', 'row', 'F:c1', 'value1', 'F:c2', 'value1'
2. Start a client to scan 'test_table', with scan.setBatch(1) and
scan.setCaching(1). The client will get one column as : {column='F:c1' and
value='value1'} in the first rpc call after scanner created, and the result
will be returned to application.
3. Before the client issues the next request, the 'region' was moved to 'rsB'
and accepted another mutations for the two columns 'c1' and 'c2' as:
> put 'test_table', 'row', 'F:c1', 'value2', 'F:c2', 'value2'
4. Then, the client will receive a RegionMovedException when issuing next
request and will retry to open scanner on 'rsB'. The newly opened scanner will
higher mvcc than old data so that could read out column as : { column='F:c2'
with value='value2'} and return the result to application.
Therefore, the application will get data as:
'row' column='F:c1' value='value1'
'row' column='F:c2', value='value2'
The returned data is combined from two different mutations and violates the
row-level transaction.
{code}
The reason is that the newly opened scanner after region moved will get a
different mvcc. I am not sure whether this result is by design for scan if
partial row result is allowed. However, such row result combined from different
transactions may make the application have unexpected state.
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