[CP] fix sql audit bug

deps/oblib/src/lib/allocator/ob_concurrent_fifo_allocator.cpp

@@ -86,6 +86,11 @@ void ObConcurrentFIFOAllocator::destroy()
   inner_allocator_.destroy();
 }
 
+void ObConcurrentFIFOAllocator::purge()
+{
+  inner_allocator_.purge();
+}
+
 void ObConcurrentFIFOAllocator::set_label(const lib::ObLabel &label)
 {
   inner_allocator_.set_label(label);

deps/oblib/src/lib/allocator/ob_concurrent_fifo_allocator.h

@@ -35,6 +35,7 @@ public:
            const lib::ObMemAttr &attr,
            const int64_t total_limit);
   void destroy();
+  void purge();
 public:
   void set_label(const lib::ObLabel &label);
   void set_attr(const lib::ObMemAttr &attr);

deps/oblib/src/lib/allocator/ob_vslice_alloc.h

@@ -103,6 +103,9 @@ public:
     purge_extra_cached_block(0, true);
     bsize_ = 0;
   }
+  void purge() {
+    purge_extra_cached_block(0);
+  }
   void set_nway(int nway) {
     if (nway <= 0) {
       nway = 1;

src/observer/mysql/ob_mysql_request_manager.h

@@ -154,7 +154,7 @@ public:
   void clear_queue()
   {
     (void)release_old(INT64_MAX);
-    allocator_.destroy();
+    allocator_.purge();
   }
 
   uint64_t get_tenant_id() const