keith-turner commented on PR #3230:
URL: https://github.com/apache/accumulo/pull/3230#issuecomment-1538685122
It may be good to move the pre upgrade checks into the Upgrader because the
current version of Accumulo may not know how to read the previous version of
Accumulo's metadata in order to perform upgrade checks. Adding new methods
make this step explicit when someone is thinking about writing a new Upgrader,
it forces them to explicity consider if conditions are safe for an upgrade.
What conditions are safe for an upgrade could be highly dependent on the two
versions of Accumulo. If its an explicit step in the Upgrader, then it makes
people consider upgrade safety in future versions of Accumulo. With all of
this in mind I made the following attempt to update the Upgrader interface.
```java
public interface Upgrader {
/**
* This method is called before {@link #upgradeZookeeper(ServerContext)}
to ensure the system is
* in a suitable state to upgrade. Examples of what this check could
attempt to do are :
*
* <UL>
* <LI>If root tablet metadata is not upgraded, ensure the root tablet is
not currently assigned
* to a live tserver.</LI>
* <LI>Ensure there are no server processes running from a previous
version of Accumulo</LI>
* </UL>
*
* <P>
* The implementation of this method is delegated to the Uprader because
it may have to read data
* from DFS and Zookeeper in formats used by previous versions of
Accumulo. This code for reading
* previous storage formats should always be delegated to the uprader.
* </P>
*
* <p>
* Any possible conditions in the distributed system that could cause the
upgrade process to
* corrupt metadata or data should be checked for here and fail if
detected.
* </p>
*
* @throws IllegalStateException if conditions are not suitable for
upgrade. The exception message
* should clearly indicate specifics about what is blocking this
upgrade step.
*/
void preUpgradeZookeeperCheck(ServerContext context);
/**
* Update entries in ZooKeeper - called before the root tablet is loaded.
*
* @param context the server context.
*/
void upgradeZookeeper(ServerContext context);
/**
* This method is called before {@link #upgradeRoot(ServerContext)} to
ensure the system is in a
* suitabl state to upgrade. Examples of what this check could attempt to
do are :
*
* <UL>
* <LI>If metadata tablets metadata is not upgraded, ensure no metadata
tablets are not currently
* assigned to a live tserver</LI>
* </UL>
*
* @throws IllegalStateException if conditions are not suitable for
upgrade. The exception message
* should clearly indicate specifics about what is blocking this
upgrade step.
*/
void preUpgradeRootCheck(ServerContext context);
/**
* Update the root tablet - called after the root tablet is loaded and
before the metadata table
* is loaded.
*
* @param context the server context.
*/
void upgradeRoot(ServerContext context);
/**
* This method is called before {@link #upgradeMetadata(ServerContext)} to
ensure the system is in
* a suitable state to upgrade. Examples of what this check could attempt
to do are :
*
* <UL>
* <LI>If user tablet metadata is not upgraded, ensure no user tablets are
not currently assigned
* to a live tserver</LI>
* </UL>
*
* @throws IllegalStateException if conditions are not suitable for
upgrade. The exception message
* should clearly indicate specifics about what is blocking this
upgrade step.
*/
void preUpgradeMetadataCheck(ServerContext context);
/**
* Update the metadata table - called after the metadata table is loaded
and before loading user
* tablets.
*
* @param context the server context.
*/
void upgradeMetadata(ServerContext context);
}
```
Would the checks written so far in the PR fit into this model?
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