tree 25220545a02b1bff80654ac41aac52e0a45658fd
parent 2fb8ebaef2beecd511e963fadbb41cbb11add138
author Zoltan Borok-Nagy <boroknagyz@cloudera.com> 1537963116 +0200
committer Impala Public Jenkins <impala-public-jenkins@cloudera.com> 1539894816 +0000

IMPALA-7543: Enhance scan ranges to support sub-ranges

This commit enhances the ScanRange class to make it possible to only
read some smaller parts of the whole ScanRange. This functionality
is needed by IMPALA-5843.

A sub-range is an offset and length which is located within the scan
range. Sub-ranges can be added to a scan range when calling
ScanRange::Reset(). If done so, the ScanRange class will only read the
parts defined by the sub-ranges.

If we have sub-ranges for a cache read then the ScanRange won't
enqueue the whole cache buffer (which contains the whole ScanRange),
but memcpy() the sub-ranges to IO/client buffers.

Smaller refactorings needed to do:
 * remove scan_range_offset_ from BufferDescriptor
 * number of bytes read are bookkeeped by ScanRange again

Testing:
 * introduced CacheReaderTestStub to fake cache reads during testing
 * extended disk-io-mgr-test.cc with sub-ranges

Change-Id: Iea26ba386713990f7671aab5a372cf449b8d51e4
Reviewed-on: http://gerrit.cloudera.org:8080/11520
Reviewed-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>