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HBASE-17730 Add documentation to upgrade coprocessors for 2.0

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Apekshit Sharma 2018-04-03 16:38:44 -07:00
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dev-support/design-docs/Coprocessor_Design_Improvements-Use_composition_instead_of_inheritance-HBASE-17732.adoc
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////
= Coprocessor Design Improvements (link:https://issues.apache.org/jira/browse/HBASE-17732[HBASE-17732])
Author: Apekshit Sharma

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src/main/asciidoc/_chapters/upgrading.adoc
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@ -546,6 +546,48 @@ The Java client API for HBase has a number of changes that break both source and
This would be a good place to link to an appendix on migrating applications
////
[[upgrade2.0.coprocessors]]
==== Upgrading Coprocessors to 2.0
Coprocessors have changed substantially in 2.0 ranging from top level design changes in class
hierarchies to changed/removed methods, interfaces, etc.
(Parent jira: link:https://issues.apache.org/jira/browse/HBASE-18169[HBASE-18169 Coprocessor fix
and cleanup before 2.0.0 release]). Some of the reasons for such widespread changes:
. Pass Interfaces instead of Implementations; e.g. TableDescriptor instead of HTableDescriptor and
Region instead of HRegion (link:https://issues.apache.org/jira/browse/HBASE-18241[HBASE-18241]
Change client.Table and client.Admin to not use HTableDescriptor).
. Design refactor so implementers need to fill out less boilerplate and so we can do more
compile-time checking (link:https://issues.apache.org/jira/browse/HBASE-17732[HBASE-17732])
. Purge Protocol Buffers from Coprocessor API
(link:https://issues.apache.org/jira/browse/HBASE-18859[HBASE-18859],
link:https://issues.apache.org/jira/browse/HBASE-16769[HBASE-16769], etc)
. Cut back on what we expose to Coprocessors removing hooks on internals that were too private to
expose (for eg. link:https://issues.apache.org/jira/browse/HBASE-18453[HBASE-18453]
CompactionRequest should not be exposed to user directly;
link:https://issues.apache.org/jira/browse/HBASE-18298[HBASE-18298] RegionServerServices Interface
cleanup for CP expose; etc)
To use coprocessors in 2.0, they should be rebuilt against new API otherwise they will fail to
load and HBase processes will die.
Suggested order of changes to upgrade the coprocessors:
. Directly implement observer interfaces instead of extending Base*Observer classes. Change
`Foo extends BaseXXXObserver` to `Foo implements XXXObserver`.
(link:https://issues.apache.org/jira/browse/HBASE-17312[HBASE-17312]).
. Adapt to design change from Inheritence to Composition
(link:https://issues.apache.org/jira/browse/HBASE-17732[HBASE-17732]) by following
link:https://github.com/apache/hbase/blob/master/dev-support/design-docs/Coprocessor_Design_Improvements-Use_composition_instead_of_inheritance-HBASE-17732.adoc#migrating-existing-cps-to-new-design[this
example].
. getTable() has been removed from the CoprocessorEnvrionment, coprocessors should self-manage
Table instances.
Some examples of writing coprocessors with new API can be found in hbase-example module
link:https://github.com/apache/hbase/tree/branch-2.0/hbase-examples/src/main/java/org/apache/hadoop/hbase/coprocessor/example[here] .
Lastly, if an api has been changed/removed that breaks you in an irreparable way, and if there's a
good justification to add it back, bring it our notice (dev@hbase.apache.org).
[[upgrade2.0.rolling.upgrades]]
==== Rolling Upgrade from 1.x to 2.x
There is no rolling upgrade from HBase 1.x+ to HBase 2.x+. In order to perform a zero downtime upgrade, you will need to run an additional cluster in parallel and handle failover in application logic.
@ -556,6 +598,7 @@ There is no rolling upgrade from HBase 1.x+ to HBase 2.x+. In order to perform a
To upgrade an existing HBase 1.x cluster, you should:
* Clean shutdown of existing 1.x cluster
* Update coprocessors
* Upgrade Master roles first
* Upgrade RegionServers
* (Eventually) Upgrade Clients