[HBASE-16747] Track memstore data size and heap overhead separately

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.0
• Component/s: regionserver
• Hadoop Flags: Incompatible change, Reviewed

Release Note

Marking it as incompatible change as there is a change in behavior for region flush decision. The default flush size of 128 MB per region was tracked against both actual data bytes size + overhead of these cells in memstore memory (Overhead because of Cell java objects and CSLM entry). As part of this jira we will keep track of cell data size only in region level. So 128 MB flush size means, 128 MB of cell data bytes (key+ value+..)

Globally we will track cell data size and heap overhead separately and will consider both for forced flushes. We will not allow over consume of heap memory by all memstore. This is as old case. Only tracking way is changed.

• Assignee: Anoop Sam John
• Reporter: Anoop Sam John
• Created: 03/Oct/16 05:57
• Updated: 01/Jul/22 21:33
• Resolved: 01/Nov/16 08:16

Description

We track the memstore size in 3 places.
1. Global at RS level in RegionServerAccounting. This tracks all memstore's size and used to calculate whether forced flushes needed because of global heap pressure
2. At region level in HRegion. This is sum of sizes of all memstores within this region. This is used to decide whether region reaches flush size (128 MB)
3. Segment level. This tracks the in memory flush/compaction decisions.

All these use the Cell's heap size which include the data bytes# as well as Cell object heap overhead. Also we include the overhead because of addition of Cells into Segment's data structures (Like CSLM).

Once we have off heap memstore, we will keep the cell data bytes in off heap area. So we can not track both data size and heap overhead as one entity. We need to separate them and track.

Proposal here is to track both cell data size and heap overhead separately at global accounting layer. As of now we have only on heap memstore. So the global memstore boundary checks will consider both (adds up and check against global max memstore size)
Track cell data size alone (This can be on heap or off heap) in region level. Region flushes use cell data size alone for the region flush decision. A user configuring 128 MB as flush size, normally he will expect to get a 128MB data flush size. But as we were including the heap overhead also, once the flush happens, the actual data size getting flushed is way behind this 128 MB. Now with this change we will behave more like what a user thinks.
Segment level in memory flush/compaction also considers cell data size alone. But we will need to track the heap overhead also. (Once the in memory flush or normal flush happens, we will have to adjust both cell data size and heap overhead)