Bug#16194302: SUPPORT FOR FLOATING-POINT SYSTEM VARIABLES

              USING THE PLUGIN INTERFACE.

ISSUE: No support for floating-point plugin
       system variables.

SOLUTION: Allowing plugins to define and expose floating-point
          system variables of type double. MYSQL_SYSVAR_DOUBLE
          and MYSQL_THDVAR_DOUBLE are added.

ISSUE: Fractional part of the def, min, max values of system
       variables are ignored.

SOLUTION: Adding functions that are used to store the raw
          representation of a double in the raw bits of unsigned
          longlong in a way that the binary representation
          remains the same.

1 files changed, 29 insertions, 2 deletions

diff --git a/storage/example/ha_example.cc b/storage/example/ha_example.cc
index c4ed4d5d2c2..68cd3fa2138 100644
--- a/storage/example/ha_example.cc
+++ b/storage/example/ha_example.cc
@@ -1004,6 +1004,7 @@ struct st_mysql_storage_engine example_storage_engine=
 
 static ulong srv_enum_var= 0;
 static ulong srv_ulong_var= 0;
+static double srv_double_var= 0;
 
 const char *enum_var_names[]=
 {
@@ -1038,9 +1039,34 @@ static MYSQL_SYSVAR_ULONG(
   1000,
   0);
 
+static MYSQL_SYSVAR_DOUBLE(
+  double_var,
+  srv_double_var,
+  PLUGIN_VAR_RQCMDARG,
+  "0.500000..1000.500000",
+  NULL,
+  NULL,
+  8.5,
+  0.5,
+  1000.5,
+  0);                             // reserved always 0
+
+static MYSQL_THDVAR_DOUBLE(
+  double_thdvar,
+  PLUGIN_VAR_RQCMDARG,
+  "0.500000..1000.500000",
+  NULL,
+  NULL,
+  8.5,
+  0.5,
+  1000.5,
+  0);
+
 static struct st_mysql_sys_var* example_system_variables[]= {
   MYSQL_SYSVAR(enum_var),
   MYSQL_SYSVAR(ulong_var),
+  MYSQL_SYSVAR(double_var),
+  MYSQL_SYSVAR(double_thdvar),
   NULL
 };
 
@@ -1051,8 +1077,9 @@ static int show_func_example(MYSQL_THD thd, struct st_mysql_show_var *var,
   var->type= SHOW_CHAR;
   var->value= buf; // it's of SHOW_VAR_FUNC_BUFF_SIZE bytes
   my_snprintf(buf, SHOW_VAR_FUNC_BUFF_SIZE,
-              "enum_var is %lu, ulong_var is %lu, %.6b", // %b is MySQL extension
-              srv_enum_var, srv_ulong_var, "really");
+              "enum_var is %lu, ulong_var is %lu, "
+              "double_var is %f, %.6b", // %b is a MySQL extension
+              srv_enum_var, srv_ulong_var, srv_double_var, "really");
   return 0;
 }