Fix for Bug #1952

"SHOW TABLE STATUS very slow w/large number of tables"
Replaced old algorithm which were used in my_dir() and stored
all information about directory entries in one chunk of memory
with new one which stores file names and MY_STAT structures in
separate memroot, so now we don't need to copy this data during
reallocation of dir_entry array.


include/my_dir.h:
  Changed mystat member of FILEINFO structure to pointer since 
  this prevents unneeded memory allocation and initialization.
  Added comment about new hidden members of MY_DIR structure.
mysys/my_lib.c:
  Replaced old algorithm in my_dir() which stored all information
  about directory entries in one chunk of memory with new one 
  which stores file names and MY_STAT structures in separate
  memroot. Now we don't copy this data during reallocation of 
  array with FILEINFO structures.
  Also tuned sizes of memory chunks during first-other
  reallocations (we suppose that we either have < 100 files 
  in the directory or > 1000 of them).
sql/sql_show.cc:
  Updated only place in code where mystat member
  of FILEINFO structure is used.

include/my_dir.h

@@ -74,14 +74,21 @@ typedef struct my_stat
 
 #endif /* USE_MY_STAT_STRUCT */
 
-typedef struct fileinfo		/* Struct returned from my_dir & my_stat */
+/* Struct describing one file returned from my_dir */
+typedef struct fileinfo
 {
   char			*name;
-  MY_STAT		mystat;
+  MY_STAT		*mystat;
 } FILEINFO;
 
 typedef struct st_my_dir	/* Struct returned from my_dir */
 {
+  /*
+    These members are just copies of parts of DYNAMIC_ARRAY structure, 
+    which is allocated right after the end of MY_DIR structure (MEM_ROOT
+    for storing names is also resides there). We've left them here because
+    we don't want to change code that uses my_dir.
+  */
   struct fileinfo	*dir_entry;
   uint			number_off_files;
 } MY_DIR;

sql/sql_show.cc

@@ -213,7 +213,7 @@ mysql_find_files(THD *thd,List<char> *files, const char *db,const char *path,
       else
 #endif
       {
-        if (file->name[0] == '.' || !MY_S_ISDIR(file->mystat.st_mode) ||
+        if (file->name[0] == '.' || !MY_S_ISDIR(file->mystat->st_mode) ||
             (wild && wild_compare(file->name,wild)))
           continue;
       }