[HBASE-18945] Make a IA.LimitedPrivate interface for CellComparator

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.0-alpha-4, 2.0.0
• Hadoop Flags: Reviewed

Release Note

CellCompartor has been added as an interface with IA.LimitedPrivate. It has the following methods
#int compare(Cell leftCell, Cell rightCell);
#int compareRows(Cell leftCell, Cell rightCell)
#int compareRows(Cell cell, byte[] bytes, int offset, int length)
#int compareWithoutRow(Cell leftCell, Cell rightCell)
#int compareFamilies(Cell leftCell, Cell rightCell
#int compareQualifiers(Cell leftCell, Cell rightCell)
#int compareTimestamps(Cell leftCell, Cell rightCell)
#int compareTimestamps(long leftCellts, long rightCellts)

This is exposed to CPs and CPs can make use of the above methods to do comparisons on the cells.
For internal usage we have CellComparatorImpl and it has static references to COMPARATOR and META_CELL_COMPARATOR.
So when a region or store is initialized we should use one of the above comparator. For META table we need the META_CELL_COMPARATOR and all other table's regions/stores will use the COMPARTOR.
While writing the comparator name in FixedFileTrailer of the Hfile we have now ensured that this rename of CellComparator.COMPARATOR/CellComparator.META_CELL_COMPARATOR to CellComparatorImpl.COMPARATOR/CellComparatorImpl.META_CELL_COMPARATOR is handled.

CellUtils is an util method that provides lot of APIs that helps to do compare, matching functionalities between two cells, or with a cell and a corrpesponding byte[] etc. Some of the APIs are internally used which will be cleaned up in a follow on JIRA HBASE-18995.

• Assignee: ramkrishna.s.vasudevan
• Reporter: ramkrishna.s.vasudevan
• Created: 05/Oct/17 05:03
• Updated: 17/Jun/22 05:23
• Resolved: 18/Oct/17 03:49

Description

Based on discussions over in HBASE-18826 and HBASE-18183 it is better we expose CellComparator as a public interface so that it could be used in Region/Store interfaces to be exposed to CPs.
Currently the Comparator is exposed in Region, STore and StoreFile. There is another discussion whether to expose it at all layers or only at Region. However since we are exposing this to CPs CellComparator being @Private is not the ideal way to do it. We have to change it to LimitedPrivate. But CellComparator has lot of additional methods which are internal (like where a Cell is compared with an incoming byte[] used in index comparsions etc).
One way to expose is that as being done now in HBASE-18826 - by exposing the return type as Comparator<Cell>. But this is not powerful. It only allows to compare cells. So we try to expose an IA.LimitedPrivate interface that is more powerful and allows comparing individual cell components also.

Issue Links

• is a child of: HBASE-18995 Move methods that are for internal usage from CellUtil to Private util class
• links to: RB link