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/* Copyright (C) 2003 MySQL AB
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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Handling of multiple key caches
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The idea is to have a thread safe hash on the table name,
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with a default key cache value that is returned if the table name is not in
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#include "mysys_priv.h"
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/*****************************************************************************
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General functions to handle SAFE_HASH objects.
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A SAFE_HASH object is used to store the hash, the mutex and default value
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needed by the rest of the key cache code.
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This is a separate struct to make it easy to later reuse the code for other
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All entries are linked in a list to allow us to traverse all elements
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and delete selected ones. (HASH doesn't allow any easy ways to do this).
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*****************************************************************************/
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Struct to store a key and pointer to object
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typedef struct st_safe_hash_entry
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struct st_safe_hash_entry *next, **prev;
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typedef struct st_safe_hash_with_default
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SAFE_HASH_ENTRY *root;
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Free a SAFE_HASH_ENTRY
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This function is called by the hash object on delete
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static void safe_hash_entry_free(SAFE_HASH_ENTRY *entry)
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DBUG_ENTER("free_assign_entry");
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my_free((uchar*) entry, MYF(0));
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/* Get key and length for a SAFE_HASH_ENTRY */
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static uchar *safe_hash_entry_get(SAFE_HASH_ENTRY *entry, size_t *length,
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my_bool not_used __attribute__((unused)))
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*length=entry->length;
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return (uchar*) entry->key;
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Init a SAFE_HASH object
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hash safe_hash handler
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elements Expected max number of elements
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default_value default value
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In case of error we set hash->default_value to 0 to allow one to call
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safe_hash_free on an object that couldn't be initialized.
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static my_bool safe_hash_init(SAFE_HASH *hash, uint elements,
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uchar *default_value)
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DBUG_ENTER("safe_hash");
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if (hash_init(&hash->hash, &my_charset_bin, elements,
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0, 0, (hash_get_key) safe_hash_entry_get,
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(void (*)(void*)) safe_hash_entry_free, 0))
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hash->default_value= 0;
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my_rwlock_init(&hash->mutex, 0);
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hash->default_value= default_value;
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Free a SAFE_HASH object
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This is safe to call on any object that has been sent to safe_hash_init()
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static void safe_hash_free(SAFE_HASH *hash)
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Test if safe_hash_init succeeded. This will also guard us against multiple
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if (hash->default_value)
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hash_free(&hash->hash);
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rwlock_destroy(&hash->mutex);
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hash->default_value=0;
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Return the value stored for a key or default value if no key
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static uchar *safe_hash_search(SAFE_HASH *hash, const uchar *key, uint length)
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DBUG_ENTER("safe_hash_search");
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rw_rdlock(&hash->mutex);
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result= hash_search(&hash->hash, key, length);
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rw_unlock(&hash->mutex);
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result= hash->default_value;
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result= ((SAFE_HASH_ENTRY*) result)->data;
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DBUG_PRINT("exit",("data: 0x%lx", (long) result));
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Associate a key with some data
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key key (path to table etc..)
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data data to to associate with the data
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This can be used both to insert a new entry and change an existing
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If one associates a key with the default key cache, the key is deleted
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1 error (Can only be EOM). In this case my_message() is called.
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static my_bool safe_hash_set(SAFE_HASH *hash, const uchar *key, uint length,
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SAFE_HASH_ENTRY *entry;
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DBUG_ENTER("safe_hash_set");
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DBUG_PRINT("enter",("key: %.*s data: 0x%lx", length, key, (long) data));
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rw_wrlock(&hash->mutex);
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entry= (SAFE_HASH_ENTRY*) hash_search(&hash->hash, key, length);
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if (data == hash->default_value)
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The key is to be associated with the default entry. In this case
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we can just delete the entry (if it existed) from the hash as a
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search will return the default entry
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if (!entry) /* nothing to do */
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/* unlink entry from list */
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if ((*entry->prev= entry->next))
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entry->next->prev= entry->prev;
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hash_delete(&hash->hash, (uchar*) entry);
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/* Entry existed; Just change the pointer to point at the new data */
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if (!(entry= (SAFE_HASH_ENTRY *) my_malloc(sizeof(*entry) + length,
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entry->key= (uchar*) (entry +1);
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memcpy((char*) entry->key, (char*) key, length);
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entry->length= length;
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/* Link entry to list */
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if ((entry->next= hash->root))
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entry->next->prev= &entry->next;
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entry->prev= &hash->root;
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if (my_hash_insert(&hash->hash, (uchar*) entry))
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/* This can only happen if hash got out of memory */
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my_free((char*) entry, MYF(0));
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rw_unlock(&hash->mutex);
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Change all entres with one data value to another data value
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new_data Change all 'old_data' to this
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We use the linked list to traverse all elements in the hash as
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this allows us to delete elements in the case where 'new_data' is the
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static void safe_hash_change(SAFE_HASH *hash, uchar *old_data, uchar *new_data)
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SAFE_HASH_ENTRY *entry, *next;
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DBUG_ENTER("safe_hash_set");
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rw_wrlock(&hash->mutex);
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for (entry= hash->root ; entry ; entry= next)
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if (entry->data == old_data)
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if (new_data == hash->default_value)
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if ((*entry->prev= entry->next))
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entry->next->prev= entry->prev;
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hash_delete(&hash->hash, (uchar*) entry);
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entry->data= new_data;
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rw_unlock(&hash->mutex);
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/*****************************************************************************
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Functions to handle the key cache objects
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*****************************************************************************/
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/* Variable to store all key cache objects */
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static SAFE_HASH key_cache_hash;
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my_bool multi_keycache_init(void)
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return safe_hash_init(&key_cache_hash, 16, (uchar*) dflt_key_cache);
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void multi_keycache_free(void)
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safe_hash_free(&key_cache_hash);
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Get a key cache to be used for a specific table.
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multi_key_cache_search()
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key key to find (usually table path)
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uint length Length of key.
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This function is coded in such a way that we will return the
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default key cache even if one never called multi_keycache_init.
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This will ensure that it works with old MyISAM clients.
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KEY_CACHE *multi_key_cache_search(uchar *key, uint length)
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if (!key_cache_hash.hash.records)
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return dflt_key_cache;
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return (KEY_CACHE*) safe_hash_search(&key_cache_hash, key, length);
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Assosiate a key cache with a key
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multi_key_cache_set()
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key key (path to table etc..)
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key_cache cache to assococite with the table
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This can be used both to insert a new entry and change an existing
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my_bool multi_key_cache_set(const uchar *key, uint length,
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KEY_CACHE *key_cache)
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return safe_hash_set(&key_cache_hash, key, length, (uchar*) key_cache);
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void multi_key_cache_change(KEY_CACHE *old_data,
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safe_hash_change(&key_cache_hash, (uchar*) old_data, (uchar*) new_data);
added
removed
mysys/mf_keycaches.c
