[GitHub] [accumulo] keith-turner commented on a diff in pull request #3429: pre load ondemand tablets for linear scans

["keith-turner (via GitHub)" <gi...@apache.org>]

keith-turner commented on code in PR #3429:
URL: https://github.com/apache/accumulo/pull/3429#discussion_r1214886547


##########
core/src/main/java/org/apache/accumulo/core/clientImpl/ClientTabletCacheImpl.java:
##########
@@ -556,15 +557,68 @@ public CachedTablet findTablet(ClientContext context, Text row, boolean skipRow,
           String.format("%.3f secs", timer.scale(SECONDS)));
     }
 
-    if (tl != null && locationNeed == LocationNeed.REQUIRED && tl.getTserverLocation().isEmpty()) {
-      requestTabletHosting(context, List.of(tl));
-      return null;
+    if (tl != null && locationNeed == LocationNeed.REQUIRED) {
+      Map<KeyExtent,CachedTablet> extentsToHost =
+          findExtentsToHost(context, minimumHostAhead * 2, hostAheadRange, lcSession, tl);
+
+      if (!extentsToHost.isEmpty()) {
+        if (extentsToHost.containsKey(tl.getExtent()) || extentsToHost.size() >= minimumHostAhead) {
+          requestTabletHosting(context, extentsToHost.values());
+        }
+      }
+
+      if (tl.getTserverLocation().isEmpty()) {
+        return null;
+      }
     }
 
     return tl;
 
   }
 
+  private Map<KeyExtent,CachedTablet> findExtentsToHost(ClientContext context, int hostAheadCount,
+      Range hostAheadRange, LockCheckerSession lcSession, CachedTablet firstTablet)
+      throws AccumuloException, TableNotFoundException, InvalidTabletHostingRequestException,
+      AccumuloSecurityException {
+    Map<KeyExtent,CachedTablet> extentsToHost;
+
+    if (hostAheadCount > 0) {
+      extentsToHost = new HashMap<>();
+      if (firstTablet.getTserverLocation().isEmpty()) {
+        extentsToHost.put(firstTablet.getExtent(), firstTablet);
+      }
+
+      KeyExtent extent = firstTablet.getExtent();
+
+      var currTablet = extent;
+
+      for (int i = 0; i < hostAheadCount; i++) {
+        if (currTablet.endRow() == null || !hostAheadRange.contains(new Key(currTablet.endRow()))) {
+          break;
+        }
+
+        CachedTablet followingTablet = _findTablet(context, currTablet.endRow(), true, false, true,
+            lcSession, LocationNeed.REQUIRED);

Review Comment:
   The method is only called when the calling method has location need of required.    I had thought of passing location need to this method and having it fail if it was not required.  I can try that and see what it looks like.



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