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Modified Upgrader11to12.upgradeZookeeper to be idempotent #5349

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Modified Upgrader11to12.upgradeZookeeper to be idempotent #5349

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28 changes: 13 additions & 15 deletions server/manager/src/main/java/org/apache/accumulo/manager/upgrade/Upgrader11to12.java
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Original file line number Diff line number Diff line change
Expand Up @@ -134,22 +134,20 @@ public void upgradeZookeeper(@NonNull ServerContext context) {

String zPath = context.getZooKeeperRoot() + Constants.ZNAMESPACES;
byte[] namespacesData = zrw.getData(zPath);
if (namespacesData.length != 0) {
throw new IllegalStateException(
"Unexpected data found under namespaces node: " + new String(namespacesData, UTF_8));
}
List<String> namespaceIdList = zrw.getChildren(zPath);
Map<String,String> namespaceMap = new HashMap<>();
for (String namespaceId : namespaceIdList) {
String namespaceNamePath = zPath + "/" + namespaceId + ZNAMESPACE_NAME;
namespaceMap.put(namespaceId, new String(zrw.getData(namespaceNamePath), UTF_8));
}
byte[] mapping = NamespaceMapping.serialize(namespaceMap);
zrw.putPersistentData(zPath, mapping, ZooUtil.NodeExistsPolicy.OVERWRITE);
if (namespacesData.length == 0) {
List<String> namespaceIdList = zrw.getChildren(zPath);
Map<String,String> namespaceMap = new HashMap<>();
for (String namespaceId : namespaceIdList) {
String namespaceNamePath = zPath + "/" + namespaceId + ZNAMESPACE_NAME;
namespaceMap.put(namespaceId, new String(zrw.getData(namespaceNamePath), UTF_8));
}
byte[] mapping = NamespaceMapping.serialize(namespaceMap);
zrw.putPersistentData(zPath, mapping, ZooUtil.NodeExistsPolicy.OVERWRITE);

for (String namespaceId : namespaceIdList) {
String namespaceNamePath = zPath + "/" + namespaceId + ZNAMESPACE_NAME;
zrw.delete(namespaceNamePath);
for (String namespaceId : namespaceIdList) {
String namespaceNamePath = zPath + "/" + namespaceId + ZNAMESPACE_NAME;
zrw.delete(namespaceNamePath);
}
Comment on lines +137 to +150
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This is nearly identical to the code suggested by @keith-turner in #4996. I replied with #4996 (comment)

In short, it is not safe to assume that a non-zero length of data here is a complete and valid mapping.

If this fails, it could have failed for any number of unpredictable reasons. The current code behavior will catch it and force the user to deal with the unique and special circumstances that apply to them. This change, however, makes a lot of assumptions about the current contents being the result of a very specific situation that you encountered due to another bug in the upgrade process. That situation has already been fixed. If this is encountered again, it is likely a completely different scenario, and you can't make assumptions about that new scenario and why it failed.

It's nice to try to make the upgrade code more idempotent, but it's very hard to do that correctly and safely. We really need to make sure the upgrade works without failing. But, if it does fail, it's more important to detect it, and troubleshoot why. We really shouldn't be making guesses here.

}

log.info("Removing problems reports from zookeeper");
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