MySQL  8.0.27
Source Code Documentation
sql_cursor.h
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22 
23 #ifndef _sql_cursor_h_
24 #define _sql_cursor_h_
25 
26 #include <stddef.h>
27 #include <sys/types.h>
28 #include <new>
29 
30 #include "sql/sql_class.h" /* Query_arena */
31 
32 class Query_result;
33 struct MEM_ROOT;
34 
35 /**
36  @file
37 
38  Declarations for implementation of server side cursors. Only
39  read-only non-scrollable cursors are currently implemented.
40 */
41 
42 /**
43  Server_side_cursor -- an interface for materialized
44  implementation of cursors. All cursors are self-contained
45  (created in their own memory root). For that reason they must
46  be deleted only using a pointer to Server_side_cursor, not to
47  its base class.
48 */
49 
51  public:
52  /**
53  For allocation of Handler objects for the temporary table. The prepared
54  statement's mem_root cannot be used, since the handler may be created and
55  deleted several times. The execution mem_root cannot be used since
56  creation of and retrieval from a cursor are in different executions.
57  */
59 
60  protected:
62  /** Row destination used for fetch */
64 
65  public:
67  : m_arena(&mem_root, Query_arena::STMT_INITIALIZED), result(result_arg) {
69  }
70  virtual bool is_open() const = 0;
71 
72  virtual bool open(THD *thd) = 0;
73  virtual bool fetch(ulong num_rows) = 0;
74  virtual void close() = 0;
76  static void *operator new(size_t size, MEM_ROOT *mem_root,
77  const std::nothrow_t & = std::nothrow) noexcept {
78  return mem_root->Alloc(size);
79  }
80  static void operator delete(void *, size_t) {}
81  static void operator delete(
82  void *, MEM_ROOT *, const std::nothrow_t &) noexcept { /* never called */
83  }
84 };
85 
87  Server_side_cursor **res);
88 
89 #endif /* _sql_cusor_h_ */
Definition: sql_class.h:234
Definition: query_result.h:55
Server_side_cursor – an interface for materialized implementation of cursors.
Definition: sql_cursor.h:50
Query_arena m_arena
Definition: sql_cursor.h:61
virtual bool fetch(ulong num_rows)=0
virtual void close()=0
MEM_ROOT mem_root
For allocation of Handler objects for the temporary table.
Definition: sql_cursor.h:58
virtual bool is_open() const =0
Query_result * result
Row destination used for fetch.
Definition: sql_cursor.h:63
virtual ~Server_side_cursor()
Definition: sql_cursor.h:75
virtual bool open(THD *thd)=0
Server_side_cursor(Query_result *result_arg)
Definition: sql_cursor.h:66
For each client connection we create a separate thread with THD serving as a thread/connection descri...
Definition: sql_class.h:821
PSI_memory_key key_memory_TABLE
Definition: psi_memory_key.cc:81
bool mysql_open_cursor(THD *thd, Query_result *result, Server_side_cursor **res)
Attempt to open a materialized cursor.
Definition: sql_cursor.cc:171
The MEM_ROOT is a simple arena, where allocations are carved out of larger blocks.
Definition: my_alloc.h:78
void * Alloc(size_t length)
Allocate memory.
Definition: my_alloc.h:135
void Clear()
Deallocate all the RAM used.
Definition: my_alloc.cc:165
Definition: result.h:29
void init_sql_alloc(PSI_memory_key key, MEM_ROOT *mem_root, size_t block_size, size_t)
Definition: thr_malloc.cc:45