[Debug](scan) Add debug log for find p0 scan coredump in pipeline (#24202)

be/src/vec/exec/scan/pip_scanner_context.h

@@ -176,6 +176,15 @@ public:
         }
     }
 
+    std::string debug_string() override {
+        auto res = ScannerContext::debug_string();
+        for (int i = 0; i < _blocks_queues.size(); ++i) {
+            res += " queue " + std::to_string(i) + ":size " +
+                   std::to_string(_blocks_queues[i].size_approx());
+        }
+        return res;
+    }
+
 private:
     int _next_queue_to_feed = 0;
     std::vector<moodycamel::ConcurrentQueue<vectorized::BlockUPtr>> _blocks_queues;

be/src/vec/exec/scan/scanner_context.h

@@ -131,7 +131,7 @@ public:
 
     bool no_schedule();
 
-    std::string debug_string();
+    virtual std::string debug_string();
 
     RuntimeState* state() { return _state; }
 

be/src/vec/exec/scan/vscan_node.cpp

@@ -279,6 +279,10 @@ Status VScanNode::get_next(RuntimeState* state, vectorized::Block* block, bool*
         return Status::OK();
     }
 
+    if (scan_block == nullptr) {
+        LOG(FATAL) << "Scan block nullptr error _context_queue_id:" << _context_queue_id
+                   << " context debug string:" << _scanner_ctx->debug_string();
+    }
     // get scanner's block memory
     block->swap(*scan_block);
     _scanner_ctx->return_free_block(std::move(scan_block));