[GitHub] [lucene-solr] madrob commented on a change in pull request #1528: SOLR-12823: remove /clusterstate.json

[GitBox <gi...@apache.org>]

madrob commented on a change in pull request #1528:
URL: https://github.com/apache/lucene-solr/pull/1528#discussion_r430596540



##########
File path: solr/core/src/java/org/apache/solr/cloud/ZkController.java
##########
@@ -491,6 +493,40 @@ public boolean isClosed() {
     assert ObjectReleaseTracker.track(this);
   }
 
+  /**
+   * <p>Verifies if /clusterstate.json exists in Zookeepeer, and if it does and is not empty, refuses to start and outputs
+   * a helpful message regarding collection migration.</p>
+   *
+   * <p>If /clusterstate.json exists and is empty, it is removed.</p>
+   */
+  private void checkNoOldClusterstate(final SolrZkClient zkClient) throws InterruptedException {
+    try {
+      if (!zkClient.exists(ZkStateReader.UNSUPPORTED_CLUSTER_STATE, true)) {
+        return;
+      }
+
+      final byte[] data = zkClient.getData(ZkStateReader.UNSUPPORTED_CLUSTER_STATE, null, null, true);
+
+      if (data.length < 5) {
+        // less than 5 chars is empty (it's likely just "{}"). This log will only occur once.
+        log.warn("{} no longer supported starting with Solr 9. Found empty file on Zookeeper, deleting it.", ZkStateReader.UNSUPPORTED_CLUSTER_STATE);
+        zkClient.delete(ZkStateReader.UNSUPPORTED_CLUSTER_STATE, -1, true);
+      } else {
+        // /clusterstate.json not empty: refuse to start but do not automatically delete. A bit of a pain but user shouldn't
+        // have older collections at this stage anyway.
+        String message = ZkStateReader.UNSUPPORTED_CLUSTER_STATE + " no longer supported starting with Solr 9. "
+            + "It is present and not empty. Cannot start Solr. Please first migrate collections to stateFormat=2 using an "
+            + "older version of Solr or if you don't care about the data then delete the file from "
+            + "Zookeeper using a command line tool, for example: bin/solr zk rm /clusterstate.json -z host:port";
+        log.error(message);
+        throw new SolrException(SolrException.ErrorCode.INVALID_STATE, message);
+      }
+    } catch (KeeperException e) {
+      log.error("", e);

Review comment:
       Makes sense. If we throw anything here it will still propagate up to SolrDispatchFilter where it will be logged, so we don't need to double up on that here. We should probably clean that up in the other places where it happens, but that's out of scope for this PR.




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