Merge pull request #72323 from ClickHouse/backport/24.8/72233

Backport #72233 to 24.8: Fix race in `GraceHashJoin`

src/Interpreters/GraceHashJoin.cpp

@@ -13,6 +13,7 @@
 #include <Core/Settings.h>
 
 #include <numeric>
+#include <shared_mutex>
 #include <fmt/format.h>
 
 
@@ -527,6 +528,7 @@ public:
     Block nextImpl() override
     {
         ExtraBlockPtr not_processed = nullptr;
+        std::shared_lock shared(eof_mutex);
 
         {
             std::lock_guard lock(extra_block_mutex);
@@ -560,7 +562,24 @@ public:
             block = left_reader.read();
             if (!block)
             {
-                return {};
+                shared.unlock();
+                bool there_are_still_might_be_rows_to_process = false;
+                {
+                    /// The following race condition could happen without this mutex:
+                    /// * we're called from `IBlocksStream::next()`
+                    /// * another thread just read the last block from `left_reader` and now is in the process of or about to call `joinBlock()`
+                    /// * it might be that `joinBlock()` will leave some rows in the `not_processed`
+                    /// * but if the current thread will return now an empty block `finished` will be set to true in `IBlocksStream::next()` and
+                    ///   these not processed rows will be lost
+                    /// So we shouldn't finish execution while there is at least one in-flight `joinBlock()` call. Let's wait until we're alone
+                    /// and double check if there are any not processed rows left.
+                    std::unique_lock exclusive(eof_mutex);
+
+                    std::lock_guard lock(extra_block_mutex);
+                    if (!not_processed_blocks.empty())
+                        there_are_still_might_be_rows_to_process = true;
+                }
+                return there_are_still_might_be_rows_to_process ? nextImpl() : Block();
             }
 
             // block comes from left_reader, need to join with right table to get the result.
@@ -595,7 +614,7 @@ public:
         return block;
     }
 
-    size_t current_bucket;
+    const size_t current_bucket;
     Buckets buckets;
     InMemoryJoinPtr hash_join;
 
@@ -606,6 +625,8 @@ public:
 
     std::mutex extra_block_mutex;
     std::list<ExtraBlockPtr> not_processed_blocks TSA_GUARDED_BY(extra_block_mutex);
+
+    std::shared_mutex eof_mutex;
 };
 
 IBlocksStreamPtr GraceHashJoin::getDelayedBlocks()

tests/queries/0_stateless/03274_grace_hash_max_joined_block_size_rows_bug.reference

@@ -0,0 +1 @@
+180	15

tests/queries/0_stateless/03274_grace_hash_max_joined_block_size_rows_bug.sql

@@ -0,0 +1,15 @@
+DROP TABLE IF EXISTS t0;
+DROP TABLE IF EXISTS t1;
+
+CREATE TABLE t0 (x UInt64) ENGINE = MergeTree ORDER BY x;
+INSERT INTO t0 SELECT number from numbers(20);
+
+CREATE TABLE t1 (x UInt64) ENGINE = MergeTree ORDER BY x;
+INSERT INTO t1 SELECT number from numbers(5, 20);
+
+SET max_joined_block_size_rows = 1;
+SET grace_hash_join_initial_buckets = 2;
+SET join_algorithm = 'grace_hash';
+
+SELECT sum(x), count() FROM t0 JOIN t1 USING x;
+