src/diskstore.c

   1 /* diskstore.c implements a very simple disk backed key-value store used
   2  * by Redis for the "disk" backend. This implementation uses the filesystem
   3  * to store key/value pairs. Every file represents a given key.
   4  *
   5  * The key path is calculated using the SHA1 of the key name. For instance
   6  * the key "foo" is stored as a file name called:
   7  *
   8  *  /0b/ee/0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33
   9  *
  10  * The couples of characters from the hex output of SHA1 are also used
  11  * to locate two two levels of directories to store the file (as most
  12  * filesystems are not able to handle too many files in a single dir).
  13  *
  14  * In the end there are 65536 final directories (256 directories inside
  15  * every 256 top level directories), so that with 1 billion of files every
  16  * directory will contain in the average 15258 entires, that is ok with
  17  * most filesystems implementation.
  18  *
  19  * Note that since Redis supports multiple databases, the actual key name
  20  * is:
  21  *
  22  *  /0b/ee/<dbid>_0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33
  23  *
  24  *  so for instance if the key is inside DB 0:
  25  *
  26  *  /0b/ee/0_0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33
  27  *
  28  * The actaul implementation of this disk store is highly dependant to the
  29  * filesystem implementation itself. This implementation may be replaced by
  30  * a B+TREE implementation in future implementations.
  31  *
  32  * Data ok every key is serialized using the same format used for .rdb
  33  * serialization. Everything is serialized on every entry: key name,
  34  * ttl information in case of keys with an associated expire time, and the
  35  * serialized value itself.
  36  *
  37  * Because the format is the same of the .rdb files it is trivial to create
  38  * an .rdb file starting from this format just by mean of scanning the
  39  * directories and concatenating entries, with the sole addition of an
  40  * .rdb header at the start and the end-of-db opcode at the end.
  41  *
  42  * -------------------------------------------------------------------------
  43  *
  44  * Copyright (c) 2010-2011, Salvatore Sanfilippo <antirez at gmail dot com>
  45  * All rights reserved.
  46  *
  47  * Redistribution and use in source and binary forms, with or without
  48  * modification, are permitted provided that the following conditions are met:
  49  *
  50  *   * Redistributions of source code must retain the above copyright notice,
  51  *     this list of conditions and the following disclaimer.
  52  *   * Redistributions in binary form must reproduce the above copyright
  53  *     notice, this list of conditions and the following disclaimer in the
  54  *     documentation and/or other materials provided with the distribution.
  55  *   * Neither the name of Redis nor the names of its contributors may be used
  56  *     to endorse or promote products derived from this software without
  57  *     specific prior written permission.
  58  *
  59  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  60  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  61  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  62  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  63  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  64  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  65  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  66  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  67  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  68  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  69  * POSSIBILITY OF SUCH DAMAGE.
  70  */
  71
  72 #include "redis.h"
  73
  74 #include <fcntl.h>
  75 #include <sys/stat.h>
  76
  77 int dsOpen(void) {
  78     struct stat sb;
  79     int retval;
  80     char *path = server.ds_path;
  81
  82     if ((retval = stat(path,&sb) == -1) && errno != ENOENT) {
  83         redisLog(REDIS_WARNING, "Error opening disk store at %s: %s",
  84                 path, strerror(errno));
  85         return REDIS_ERR;
  86     }
  87
  88     /* Directory already in place. Assume everything is ok. */
  89     if (retval == 0 && S_ISDIR(sb.st_mode)) return REDIS_OK;
  90
  91     /* File exists but it's not a directory */
  92     if (retval == 0 && !S_ISDIR(sb.st_mode)) {
  93         redisLog(REDIS_WARNING,"Disk store at %s is not a directory", path);
  94         return REDIS_ERR;
  95     }
  96
  97     /* New disk store, create the directory structure now, as creating
  98      * them in a lazy way is not a good idea, after very few insertions
  99      * we'll need most of the 65536 directories anyway. */
 100     if (mkdir(path) == -1) {
 101         redisLog(REDIS_WARNING,"Disk store init failed creating dir %s: %s",
 102             path, strerror(errno));
 103         return REDIS_ERR;
 104     }
 105     return REDIS_OK;
 106 }
 107
 108 int dsClose(void) {
 109     return REDIS_OK;
 110 }
 111
 112 int dsSet(redisDb *db, robj *key, robj *val) {
 113 }
 114
 115 robj *dsGet(redisDb *db, robj *key) {
 116 }
 117
 118 int dsDel(redisDb *db, robj *key) {
 119 }
 120
 121 int dsExists(redisDb *db, robj *key) {
 122 }