[GitHub] [pulsar] merlimat commented on a diff in pull request #17264: [improve][broker]Recover as much cursor data as possible, even if entry is invalid

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

merlimat commented on code in PR #17264:
URL: https://github.com/apache/pulsar/pull/17264#discussion_r959005384


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managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedCursorImpl.java:
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@@ -553,6 +505,66 @@ protected void recoverFromLedger(final ManagedCursorInfo info, final VoidCallbac
         }
     }
 
+    private void recoverCursorByLedgerEntry(long entryId, VoidCallback callback, ManagedCursorInfo info,
+                                            LedgerHandle recoveredFromCursorLedger){
+        recoveredFromCursorLedger.asyncReadEntries(entryId, entryId, (rc1, lh1, seq, ctx1) -> {
+            if (log.isDebugEnabled()) {
+                log.debug("[{}} readComplete rc={} entryId={}", ledger.getName(), rc1, lh1.getLastAddConfirmed());
+            }
+            boolean tryPreviousEntry = Code.NoSuchEntryException == rc1 && entryId > 0;
+            if (tryPreviousEntry) {
+                recoverCursorByLedgerEntry(entryId - 1, callback, info, recoveredFromCursorLedger);

Review Comment:
   If all the entries are not available, this might take a significant amount of time, since we're trying each and every entry. 
   
   Even if it's not perfect, it would be better to try a binary-search approach to find the highest entry that is readable.



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