diff --git a/hbase-common/src/main/resources/hbase-default.xml b/hbase-common/src/main/resources/hbase-default.xml
index ea18892015c..4c16b69639d 100644
--- a/hbase-common/src/main/resources/hbase-default.xml
+++ b/hbase-common/src/main/resources/hbase-default.xml
@@ -691,7 +691,30 @@ possible configurations would overwhelm and obscure the important.
Enables the MemStore-Local Allocation Buffer,
a feature which works to prevent heap fragmentation under
heavy write loads. This can reduce the frequency of stop-the-world
- GC pauses on large heaps.
+ GC pauses on large heaps.
+
+
+
+ hbase.hregion.memstore.mslab.chunksize
+ 2097152
+ The maximum byte size of a chunk in the MemStoreLAB. Unit: bytes
+
+
+ hbase.regionserver.offheap.global.memstore.size
+ 0
+ The amount of off-heap memory all MemStores in a RegionServer may use.
+ A value of 0 means that no off-heap memory will be used and all chunks in MSLAB
+ will be HeapByteBuffer, otherwise the non-zero value means how many megabyte of
+ off-heap memory will be used for chunks in MSLAB and all chunks in MSLAB will be
+ DirectByteBuffer. Unit: megabytes.
+
+
+
+ hbase.hregion.memstore.mslab.max.allocation
+ 262144
+ The maximal size of one allocation in the MemStoreLAB, if the desired byte
+ size exceed this threshold then it will be just allocated from JVM heap rather than MemStoreLAB.
+
hbase.hregion.max.filesize
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/DefaultMemStore.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/DefaultMemStore.java
index 8570c22613d..a50d0fc34e8 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/DefaultMemStore.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/DefaultMemStore.java
@@ -160,19 +160,23 @@ public class DefaultMemStore extends AbstractMemStore {
getNextRow(cell, this.snapshot.getCellSet()));
}
- @Override public void updateLowestUnflushedSequenceIdInWAL(boolean onlyIfMoreRecent) {
+ @Override
+ public void updateLowestUnflushedSequenceIdInWAL(boolean onlyIfMoreRecent) {
}
- @Override protected boolean preUpdate(MutableSegment currentActive, Cell cell,
+ @Override
+ protected boolean preUpdate(MutableSegment currentActive, Cell cell,
MemStoreSizing memstoreSizing) {
return true;
}
- @Override protected void postUpdate(MutableSegment currentActive) {
+ @Override
+ protected void postUpdate(MutableSegment currentActive) {
return;
}
- @Override protected boolean sizeAddedPreOperation() {
+ @Override
+ protected boolean sizeAddedPreOperation() {
return false;
}
@@ -186,7 +190,8 @@ public class DefaultMemStore extends AbstractMemStore {
return HConstants.NO_SEQNUM;
}
- @Override public boolean isSloppy() {
+ @Override
+ public boolean isSloppy() {
return false;
}
diff --git a/src/main/asciidoc/_chapters/offheap_read_write.adoc b/src/main/asciidoc/_chapters/offheap_read_write.adoc
index dad8ed08d13..44ee97c2458 100644
--- a/src/main/asciidoc/_chapters/offheap_read_write.adoc
+++ b/src/main/asciidoc/_chapters/offheap_read_write.adoc
@@ -183,4 +183,23 @@ Please also see: link:https://issues.apache.org/jira/browse/HBASE-22483[HBASE-22
[[regionserver.offheap.writepath]]
== Offheap write-path
-TODO
+In HBase 2.0.0, link:https://issues.apache.org/jira/browse/HBASE-15179[HBASE-15179] made the HBase write path to work off-heap. By default, the MemStores use
+MSLAB to avoid memory fragmentation. It creates bigger fixed sized chunks and memstore cell's data will get copied into these chunks. These chunks can be pooled
+also and from 2.0.0 the MSLAB (MemStore-Local Allocation Buffer) pool is by default ON. Write off-heaping makes use of the MSLAB pool. It creates MSLAB chunks
+as Direct ByteBuffers and pools them. HBase defaults to using no off-heap memory for MSLAB which means that cells are copied to heap chunk in MSLAB by default
+rather than off-heap chunk.
+
+`hbase.regionserver.offheap.global.memstore.size` is the configuration key which controls the amount of off-heap data whose value is the number of megabytes
+of off-heap memory that should be by MSLAB (e.g. `25` would result in 25MB of off-heap). Be sure to increase `HBASE_OFFHEAPSIZE` which will set the JVM's
+MaxDirectMemorySize property. Its default value is 0, means MSLAB use heap chunks.
+
+`hbase.hregion.memstore.mslab.chunksize` controls the size of each off-heap chunk, defaulting to `2097152` (2MB).
+
+When a Cell is added to a MemStore, the bytes for that Cell are copied into these off-heap buffers (if set the `hbase.regionserver.offheap.global.memstore.size` to non-zero)
+and a Cell POJO will refer to this memory area. This can greatly reduce the on-heap occupancy of the MemStores and reduce the total heap utilization for RegionServers
+in a write-heavy workload. On-heap and off-heap memory utiliazation are tracked at multiple levels to implement low level and high level memory management.
+The decision to flush a MemStore considers both the on-heap and off-heap usage of that MemStore. At the Region level, the sum of the on-heap and off-heap usages and
+compares them against the region flush size (128MB, by default). Globally, on-heap size occupancy of all memstores are tracked as well as off-heap size. When any of
+these sizes breaches the lower mark (`hbase.regionserver.global.memstore.size.lower.limit`) or the maximum size `hbase.regionserver.global.memstore.size`), all
+regions are selected for forced flushes.
+