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HBASE-20060 Add details of off heap memstore into book. (#334)

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openinx 2019-06-26 14:58:34 +08:00 committed by GitHub
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3 changed files with 54 additions and 7 deletions
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25
hbase-common/src/main/resources/hbase-default.xml
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@ -696,7 +696,30 @@ possible configurations would overwhelm and obscure the important.
Enables the MemStore-Local Allocation Buffer, Enables the MemStore-Local Allocation Buffer,
a feature which works to prevent heap fragmentation under a feature which works to prevent heap fragmentation under
heavy write loads. This can reduce the frequency of stop-the-world heavy write loads. This can reduce the frequency of stop-the-world
GC pauses on large heaps.</description> GC pauses on large heaps.
</description>
</property>
<property>
<name>hbase.hregion.memstore.mslab.chunksize</name>
<value>2097152</value>
<description>The maximum byte size of a chunk in the MemStoreLAB. Unit: bytes</description>
</property>
<property>
<name>hbase.regionserver.offheap.global.memstore.size</name>
<value>0</value>
<description>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.
</description>
</property>
<property>
<name>hbase.hregion.memstore.mslab.max.allocation</name>
<value>262144</value>
<description>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.
</description>
</property> </property>
<property> <property>
<name>hbase.hregion.max.filesize</name> <name>hbase.hregion.max.filesize</name>

15
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/DefaultMemStore.java
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@ -160,19 +160,23 @@ public class DefaultMemStore extends AbstractMemStore {
getNextRow(cell, this.snapshot.getCellSet())); 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) { MemStoreSizing memstoreSizing) {
return true; return true;
} }
@Override protected void postUpdate(MutableSegment currentActive) { @Override
protected void postUpdate(MutableSegment currentActive) {
return; return;
} }
@Override protected boolean sizeAddedPreOperation() { @Override
protected boolean sizeAddedPreOperation() {
return false; return false;
} }
@ -186,7 +190,8 @@ public class DefaultMemStore extends AbstractMemStore {
return HConstants.NO_SEQNUM; return HConstants.NO_SEQNUM;
} }
@Override public boolean isSloppy() { @Override
public boolean isSloppy() {
return false; return false;
} }

21
src/main/asciidoc/_chapters/offheap_read_write.adoc
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@ -183,4 +183,23 @@ Please also see: link:https://issues.apache.org/jira/browse/HBASE-22483[HBASE-22
[[regionserver.offheap.writepath]] [[regionserver.offheap.writepath]]
== Offheap write-path == 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.