liu ming created TRAFODION-1729:
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Summary: change the coprocessor deployment method
Key: TRAFODION-1729
URL: https://issues.apache.org/jira/browse/TRAFODION-1729
Project: Apache Trafodion
Issue Type: Improvement
Components: dtm
Reporter: liu ming
I have a proposal to change our current HBase coprocessor configuration method.
There are three ways to add a coprocessor to a HBase table:
1. Via editing hbase-site.xml, which will load coprocessor for ALL tables
(Trafodion is using this method now)
2. Via HBase shell command
3. Via HTableDescriptor.addCoprocessor() java API
Trafodion now is using the first method. I proposed to use method 3, I finished
a prototype and test seems works well.
Here are the reasons I propose for this change:
At present, the Trafodion installer needs to modify the hbase-site.xml and then
restart HBase instance for the configuration to take effect. This step not only
complicate the installer but also let user think Trafodion is intrusive into
underlying HBase system. It will be ideal if we can avoid this step. Another
problem: in CDH, there is a concept called ‘region server group’ or something,
so the settings will have to carefully handled by installer to apply to all
groups. As we saw recently in WebRoot deployment, Trafodion failed due to this
reason. All these are very error prone and complicate the Trafodion installer.
Once CDH or HDP changed something, Trafodion may fail again.
So I spent time to investigate why we need to restart HBase in order to install
Trafodion.
As I understand, there are 3 major reasons
1. To add hbase-trx coprocessors
2. To overload HRegion with TransactionalRegion
3. Various configuration settings, need to check one by one.
The first configuration can be avoided by applying my proposed change.
The second one, I look through the TransactionalRegion.java, and find out the
only reason (now) is to overload the getScanner() method to be public so can be
invoked by the coprocessor. And there are only 1 or 2 places that API is
invoked in Trafodion code. I checked with Kevin and he proposed by using ‘java
reflection’ we can also avoid this.
All other configuration items to some extent look like ‘best to have’, but not
‘must to have’. And I also find two config items seems never been used:
hbase.bulkload.staging.dir /hbase-staging (Suresh can confirm, but
I search in all code, seems this is never used)
hbase.regionserver.region.transactional.tlog true (Narendra can confirm,
this is NEVER used, maybe a legacy config item?)
Yes, by now, there are still some other config items seems cannot be avoided,
but I hope we can find some way to remove them in the future. I am not trying
to solve all issues right now, just want to start the effort to remove
unnecessary hbase reconfiguration.
For this example, Coprocessors can be added to a table at run time, no need to
edit the hbase-site.xml and restart hbase. This is only the first step to try
to remove the deep impact to the current HBase config and restart HBase.
So I asked for your opinions about this change. If you think this is necessary,
I will continue to file a JIRA and fix it.
I strongly recommend to get rid of the step of ‘modify hbase-site.xml and
restart your hbase’ for Trafodion installation, it should be an option , to
tune the system to best suit Trafodion, but should not be a forced step. To be
note: Apache Phoenix is also a SQL on HBase, its installation will change
nothing of underlying HBase, very lightweight, no ‘intrude into’ the existing
HBase system. Trafodion is considered to be heavy and intrusive in this manner,
and I feel maybe we can change this.
Should I start this discussion in the dev mail list?
P.S. a list of changed config items. My proposal will remove the last one, hope
we can get rid of all of them:
hbase.master.distributed.log.splitting false
hbase.snapshot.master.timeoutMillis 600000
hbase_regionserver_lease_period 600000
hbase.hregion.impl
org.apache.hadoop.hbase.regionserver.transactional.TransactionalRegion
hbase.regionserver.region.split.policy
org.apache.hadoop.hbase.regionserver.ConstantSizeRegionSplitPolicy
hbase.snapshot.enabled true
hbase.bulkload.staging.dir /hbase-staging
hbase.regionserver.region.transactional.tlog true
hbase.snapshot.region.timeout 600000
hbase_coprocessor_region_classes
org.apache.hadoop.hbase.coprocessor.transactional.TrxRegionObserver,org.apache.hadoop.hbase.coprocessor.transactional.TrxRegionEndpoint,org.apache.hadoop.hbase.coprocessor.AggregateImplementation
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