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MDEV-31721: Cursor protocol increases the counter of "Empty_queries" for select

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Problem:
  Empty queries are incremented if no rows are sent to the client in the
  EXECUTE phase of select query. With cursor protocol, rows are not sent
  during EXECUTE phase; they are sent later in FETCH phase. Hence,
  queries executed with cursor protocol are always falsely treated as
  empty in EXECUTE phase.

Fix:
  For cursor protocol, empty queries are now counted during the FETCH
  phase. This ensures counter correctly reflects whether any rows were
  actually sent to the client.

Tests included in `mysql-test/main/show.test`.
This commit is contained in:
Raghunandan Bhat
2025-06-24 12:59:16 +05:30
committed by Raghunandan Bhat
parent 7ab205b009
commit 2c7cea28da
8 changed files with 154 additions and 67 deletions
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66
sql/sql_cursor.cc
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@@ -24,72 +24,6 @@
#include "probes_mysql.h"
#include "sql_parse.h" // mysql_execute_command
/****************************************************************************
Declarations.
****************************************************************************/
/**
Materialized_cursor -- an insensitive materialized server-side
cursor. The result set of this cursor is saved in a temporary
table at open. The cursor itself is simply an interface for the
handler of the temporary table.
*/
class Materialized_cursor: public Server_side_cursor
{
MEM_ROOT main_mem_root;
/* A fake unit to supply to select_send when fetching */
SELECT_LEX_UNIT fake_unit;
TABLE *table;
List<Item> item_list;
ulong fetch_limit;
ulong fetch_count;
bool is_rnd_inited;
public:
Materialized_cursor(select_result *result, TABLE *table);
int send_result_set_metadata(THD *thd, List<Item> &send_result_set_metadata);
bool is_open() const override { return table != 0; }
int open(JOIN *join __attribute__((unused))) override;
void fetch(ulong num_rows) override;
void close() override;
bool export_structure(THD *thd, Row_definition_list *defs) override
{
return table->export_structure(thd, defs);
}
~Materialized_cursor() override;
void on_table_fill_finished();
};
/**
Select_materialize -- a mediator between a cursor query and the
protocol. In case we were not able to open a non-materialzed
cursor, it creates an internal temporary HEAP table, and insert
all rows into it. When the table reaches max_heap_table_size,
it's converted to a MyISAM table. Later this table is used to
create a Materialized_cursor.
*/
class Select_materialize: public select_unit
{
select_result *result; /**< the result object of the caller (PS or SP) */
public:
Materialized_cursor *materialized_cursor;
Select_materialize(THD *thd_arg, select_result *result_arg):
select_unit(thd_arg), result(result_arg), materialized_cursor(0) {}
bool send_result_set_metadata(List<Item> &list, uint flags) override;
bool send_eof() override { return false; }
bool view_structure_only() const override
{
return result->view_structure_only();
}
};
/**************************************************************************/
/**
Attempt to open a materialized cursor.