From 4543777f35c936c0e5fabf30ab0cb57a953550ac Mon Sep 17 00:00:00 2001
From: Elliotte Rusty Harold <elharo@users.noreply.github.com>
Date: Tue, 24 Sep 2024 15:03:44 -0400
Subject: [PATCH] Bug hunting

---
 .../presto/server/protocol/Query.java         | 15 +++++++++++
 .../presto/server/protocol/RowIterable.java   | 25 +++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/presto-main/src/main/java/com/facebook/presto/server/protocol/Query.java b/presto-main/src/main/java/com/facebook/presto/server/protocol/Query.java
index c944f0cd468b..173497579c6e 100644
--- a/presto-main/src/main/java/com/facebook/presto/server/protocol/Query.java
+++ b/presto-main/src/main/java/com/facebook/presto/server/protocol/Query.java
@@ -22,6 +22,7 @@
 import com.facebook.presto.client.StatementStats;
 import com.facebook.presto.common.ErrorCode;
 import com.facebook.presto.common.Page;
+import com.facebook.presto.common.block.Block;
 import com.facebook.presto.common.block.BlockEncodingSerde;
 import com.facebook.presto.common.transaction.TransactionId;
 import com.facebook.presto.common.type.BooleanType;
@@ -445,6 +446,19 @@ else if (queryManager.getQueryRetryCount(queryId) == 1 && retryQueryWithHistoryB
                 queryResults.getUpdateCount());
     }
 
+    private static void validateBlockSizesInPage(Page page)
+    {
+        // debugging
+        for (int channel = 0; channel < page.getChannelCount(); channel++) {
+            Block block = page.getBlock(channel);
+            if (block.getPositionCount() != page.getPositionCount()) {
+                throw new IllegalArgumentException(
+                        format("Wrongly sized block: channel: %d block poition count: %d page position count: %d %s",
+                                channel, block.getPositionCount(), page.getPositionCount(), block.getClass().getCanonicalName()));
+            }
+        }
+    }
+
     private synchronized QueryResults getNextResult(long token, UriInfo uriInfo, String scheme, DataSize targetResultSize, boolean binaryResults)
     {
         // check if the result for the token have already been created
@@ -502,6 +516,7 @@ private synchronized QueryResults getNextResult(long token, UriInfo uriInfo, Str
                     }
 
                     Page page = serde.deserialize(serializedPage);
+                    validateBlockSizesInPage(page);
                     bytes += page.getLogicalSizeInBytes();
                     rows += page.getPositionCount();
                     pages.add(new RowIterable(session.toConnectorSession(), types, page));
diff --git a/presto-main/src/main/java/com/facebook/presto/server/protocol/RowIterable.java b/presto-main/src/main/java/com/facebook/presto/server/protocol/RowIterable.java
index 9d1de7a65eef..e4dd04eda36f 100644
--- a/presto-main/src/main/java/com/facebook/presto/server/protocol/RowIterable.java
+++ b/presto-main/src/main/java/com/facebook/presto/server/protocol/RowIterable.java
@@ -25,6 +25,7 @@
 import java.util.Iterator;
 import java.util.List;
 
+import static java.lang.String.format;
 import static java.util.Objects.requireNonNull;
 
 class RowIterable
@@ -39,6 +40,8 @@ class RowIterable
         this.session = session;
         this.types = ImmutableList.copyOf(requireNonNull(types, "types is null"));
         this.page = requireNonNull(page, "page is null");
+
+        validateBlockSizesInPage(page);
     }
 
     @Override
@@ -60,6 +63,8 @@ private RowIterator(ConnectorSession session, List<Type> types, Page page)
             this.session = session;
             this.types = types;
             this.page = page;
+
+            validateBlockSizesInPage(page);
         }
 
         @Override
@@ -74,9 +79,29 @@ protected List<Object> computeNext()
             for (int channel = 0; channel < page.getChannelCount(); channel++) {
                 Type type = types.get(channel);
                 Block block = page.getBlock(channel);
+                // Caused by: java.lang.IllegalArgumentException: Invalid position 1 in block with 1 positions
+                // why does block onlly have one position when we're asking for at least 12?
+                // It's not an off by one error. It's that there's only one row ID in the block.
+                // That's why it works with LIMIT 1 and not LIMIT 2
+                // maybe an issue with compressed dictionary blocks or something like that?
+                // only some tables/rows use dictionary blocks
+                // and exception changes from LIMIT 2 to 3
                 values.add(type.getObjectValue(session.getSqlFunctionProperties(), block, position));
             }
             return Collections.unmodifiableList(values);
         }
     }
+
+    private static void validateBlockSizesInPage(Page page)
+    {
+        // debugging
+        for (int channel = 0; channel < page.getChannelCount(); channel++) {
+            Block block = page.getBlock(channel);
+            if (block.getPositionCount() != page.getPositionCount()) {
+                throw new IllegalArgumentException(
+                    format("Wrongly sized block: channel: %d block poition count: %d page position count: %d %s",
+                    channel, block.getPositionCount(), page.getPositionCount(), block.getClass().getCanonicalName()));
+            }
+        }
+    }
 }