mf_keycaches.c 8.47 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
/* Copyright (C) 2003 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*
  Handling of multiple key caches

  The idea is to have a thread safe hash on the table name,
  with a default key cache value that is returned if the table name is not in
  the cache.
*/

#include "mysys_priv.h"
26
#include <keycache.h>
27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161
#include <hash.h>
#include <m_string.h>

/*****************************************************************************
  General functions to handle SAFE_HASH objects.

  A SAFE_HASH object is used to store the hash, the mutex and default value
  needed by the rest of the key cache code.
  This is a separate struct to make it easy to later reuse the code for other
  purposes

  All entries are linked in a list to allow us to traverse all elements
  and delete selected ones. (HASH doesn't allow any easy ways to do this).
*****************************************************************************/

/*
  Struct to store a key and pointer to object
*/

typedef struct st_safe_hash_entry
{
  byte *key;
  uint length;
  byte *data;
  struct st_safe_hash_entry *next, **prev;
} SAFE_HASH_ENTRY;


typedef struct st_safe_hash_with_default
{
#ifdef THREAD
  rw_lock_t mutex;
#endif
  HASH hash;
  byte *default_value;
  SAFE_HASH_ENTRY *root;
} SAFE_HASH;


/*
  Free a SAFE_HASH_ENTRY

  This function is called by the hash object on delete
*/

static void safe_hash_entry_free(SAFE_HASH_ENTRY *entry)
{
  DBUG_ENTER("free_assign_entry");
  my_free((gptr) entry, MYF(0));
  DBUG_VOID_RETURN;
}


/* Get key and length for a SAFE_HASH_ENTRY */

static byte *safe_hash_entry_get(SAFE_HASH_ENTRY *entry, uint *length,
				 my_bool not_used __attribute__((unused)))
{
  *length=entry->length;
  return (byte*) entry->key;
}


/*
  Init a SAFE_HASH object

  SYNOPSIS
    safe_hash_init()
    hash		safe_hash handler
    elements		Expected max number of elements
    default_value	default value

  NOTES
    In case of error we set hash->default_value to 0 to allow one to call
    safe_hash_free on an object that couldn't be initialized.

  RETURN
    0  ok
    1  error
*/

static my_bool safe_hash_init(SAFE_HASH *hash, uint elements,
			      byte *default_value)
{
  DBUG_ENTER("safe_hash");
  if (hash_init(&hash->hash, &my_charset_bin, elements,
		0, 0, (hash_get_key) safe_hash_entry_get,
		(void (*)(void*)) safe_hash_entry_free, 0))
  {
    hash->default_value= 0;
    DBUG_RETURN(1);
  }
  my_rwlock_init(&hash->mutex, 0);
  hash->default_value= default_value;
  hash->root= 0;
  DBUG_RETURN(0);
}


/*
  Free a SAFE_HASH object

  NOTES
    This is safe to call on any object that has been sent to safe_hash_init()
*/

static void safe_hash_free(SAFE_HASH *hash)
{
  /*
    Test if safe_hash_init succeeded. This will also guard us against multiple
    free calls.
  */
  if (hash->default_value)
  {
    hash_free(&hash->hash);
    rwlock_destroy(&hash->mutex);
    hash->default_value=0;
  }
}

/*
  Return the value stored for a key or default value if no key
*/

static byte *safe_hash_search(SAFE_HASH *hash, const byte *key, uint length)
{
  byte *result;
  DBUG_ENTER("safe_hash_search");
  rw_rdlock(&hash->mutex);
  result= hash_search(&hash->hash, key, length);
  rw_unlock(&hash->mutex);
  if (!result)
    result= hash->default_value;
  else
    result= ((SAFE_HASH_ENTRY*) result)->data;
162
  DBUG_PRINT("exit",("data: 0x%lx", result));
163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192
  DBUG_RETURN(result);
}


/*
  Associate a key with some data

  SYONOPSIS
    safe_hash_set()
    hash			Hash handle
    key				key (path to table etc..)
    length			Length of key
    data			data to to associate with the data

  NOTES
    This can be used both to insert a new entry and change an existing
    entry.
    If one associates a key with the default key cache, the key is deleted

  RETURN
    0  ok
    1  error (Can only be EOM). In this case my_message() is called.
*/

static my_bool safe_hash_set(SAFE_HASH *hash, const byte *key, uint length,
			     byte *data)
{
  SAFE_HASH_ENTRY *entry;
  my_bool error= 0;
  DBUG_ENTER("safe_hash_set");
193
  DBUG_PRINT("enter",("key: %.*s  data: 0x%lx", length, key, data));
194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237

  rw_wrlock(&hash->mutex);
  entry= (SAFE_HASH_ENTRY*) hash_search(&hash->hash, key, length);

  if (data == hash->default_value)
  {
    /*
      The key is to be associated with the default entry. In this case
      we can just delete the entry (if it existed) from the hash as a
      search will return the default entry
    */
    if (!entry)					/* nothing to do */
      goto end;
    /* unlink entry from list */
    if ((*entry->prev= entry->next))
      entry->next->prev= entry->prev;
    hash_delete(&hash->hash, (byte*) entry);
    goto end;
  }
  if (entry)
  {
    /* Entry existed;  Just change the pointer to point at the new data */
    entry->data= data;
  }
  else
  {
    if (!(entry= (SAFE_HASH_ENTRY *) my_malloc(sizeof(*entry) + length,
					       MYF(MY_WME))))
    {
      error= 1;
      goto end;
    }
    entry->key= (byte*) (entry +1);
    memcpy((char*) entry->key, (char*) key, length);
    entry->length= length;
    entry->data= data;
    /* Link entry to list */
    if ((entry->next= hash->root))
      entry->next->prev= &entry->next;
    entry->prev= &hash->root;
    hash->root= entry;
    if (my_hash_insert(&hash->hash, (byte*) entry))
    {
      /* This can only happen if hash got out of memory */
ingo@mysql.com's avatar
ingo@mysql.com committed
238
      my_free((char*) entry, MYF(0));
239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298
      error= 1;
      goto end;
    }
  }

end:
  rw_unlock(&hash->mutex);
  DBUG_RETURN(error);
}


/*
  Change all entres with one data value to another data value

  SYONOPSIS
    safe_hash_change()
    hash			Hash handle
    old_data			Old data
    new_data			Change all 'old_data' to this

  NOTES
    We use the linked list to traverse all elements in the hash as
    this allows us to delete elements in the case where 'new_data' is the
    default value.
*/

static void safe_hash_change(SAFE_HASH *hash, byte *old_data, byte *new_data)
{
  SAFE_HASH_ENTRY *entry, *next;
  DBUG_ENTER("safe_hash_set");

  rw_wrlock(&hash->mutex);

  for (entry= hash->root ; entry ; entry= next)
  {
    next= entry->next;
    if (entry->data == old_data)
    {
      if (new_data == hash->default_value)
	hash_delete(&hash->hash, (byte*) entry);
      else
	entry->data= new_data;
    }
  }

  rw_unlock(&hash->mutex);
  DBUG_VOID_RETURN;
}


/*****************************************************************************
  Functions to handle the key cache objects
*****************************************************************************/

/* Variable to store all key cache objects */
static SAFE_HASH key_cache_hash;


my_bool multi_keycache_init(void)
{
299
  return safe_hash_init(&key_cache_hash, 16, (byte*) dflt_key_cache);
300 301 302 303 304 305 306 307 308 309 310 311
}


void multi_keycache_free(void)
{
  safe_hash_free(&key_cache_hash);
}

/*
  Get a key cache to be used for a specific table.

  SYNOPSIS
312
    multi_key_cache_search()
313 314 315 316 317 318 319 320 321 322 323 324
    key				key to find (usually table path)
    uint length			Length of key.

  NOTES
    This function is coded in such a way that we will return the
    default key cache even if one never called multi_keycache_init.
    This will ensure that it works with old MyISAM clients.

  RETURN
    key cache to use
*/

325
KEY_CACHE *multi_key_cache_search(byte *key, uint length)
326 327
{
  if (!key_cache_hash.hash.records)
328 329
    return dflt_key_cache;
  return (KEY_CACHE*) safe_hash_search(&key_cache_hash, key, length);
330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349
}


/*
  Assosiate a key cache with a key


  SYONOPSIS
    multi_key_cache_set()
    key				key (path to table etc..)
    length			Length of key
    key_cache			cache to assococite with the table

  NOTES
    This can be used both to insert a new entry and change an existing
    entry
*/


my_bool multi_key_cache_set(const byte *key, uint length,
350
			    KEY_CACHE *key_cache)
351 352 353 354 355
{
  return safe_hash_set(&key_cache_hash, key, length, (byte*) key_cache);
}


356 357
void multi_key_cache_change(KEY_CACHE *old_data,
			    KEY_CACHE *new_data)
358 359 360
{
  safe_hash_change(&key_cache_hash, (byte*) old_data, (byte*) new_data);
}