DomGarguilo commented on a change in pull request #2320:
URL: https://github.com/apache/accumulo/pull/2320#discussion_r752613701



##########
File path: 
server/tserver/src/main/java/org/apache/accumulo/tserver/TabletServer.java
##########
@@ -791,6 +798,50 @@ public void run() {
       }
     }, 0, 5000, TimeUnit.MILLISECONDS);
 
+    // Periodically check that metadata of tablets matches what is held in 
memory
+    
ThreadPools.createGeneralScheduledExecutorService(aconf).scheduleWithFixedDelay(()
 -> {
+      final SortedMap<KeyExtent,Tablet> onlineTabletsSnapshot = 
onlineTablets.snapshot();
+
+      final SortedSet<KeyExtent> userTablets = new TreeSet<>();
+      final SortedSet<KeyExtent> nonUserTablets = new TreeSet<>();
+
+      // Create subsets of tablets based on DataLevel: one set who's DataLevel 
is USER and another
+      // containing the remaining tablets (those who's DataLevel is ROOT or 
METADATA).
+      // This needs to happen so we can use .readTablets() on the 
DataLevel.USER tablets in order
+      // to reduce RPCs.
+      // TODO: Push this partitioning, based on DataLevel, to ample.
+      onlineTabletsSnapshot.forEach((k, v) -> {
+        if (Ample.DataLevel.of(k.tableId()) == Ample.DataLevel.USER) {
+          userTablets.add(k);
+        } else {
+          nonUserTablets.add(k);
+        }
+      });
+
+      List<TabletMetadata> tmdList;
+
+      // gather metadata for all tablets with DataLevel.USER using 
readTablets()
+      try (TabletsMetadata tabletsMetadata = 
getContext().getAmple().readTablets()
+          .forTablets(userTablets).fetch(FILES, LOGS, ECOMP, 
PREV_ROW).build()) {
+        tmdList = new 
ArrayList<>(IteratorUtils.toList(tabletsMetadata.iterator()));
+      }
+
+      // gather metadata for all tablets with DataLevel.ROOT or METADATA using 
readTablet()
+      nonUserTablets.forEach(extent -> {
+        TabletMetadata tabletMetadata =
+            getContext().getAmple().readTablet(extent, FILES, LOGS, ECOMP, 
PREV_ROW);
+        tmdList.add(tabletMetadata);
+      });
+
+      // for each tablet, compare its metadata to what is held in memory
+      for (TabletMetadata tabletMetadata : tmdList) {

Review comment:
       Do you think it would suffice to check that each KeyExtent in 
onlineTabletsSnapshot is present within one of the returned TabletMetadata? I'm 
not too sure what other data you might be referring to. @keith-turner 




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