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 #include "sha1.h"
  74
  75 #include <fcntl.h>
  76 #include <sys/stat.h>
  77 #include <dirent.h>
  78
  79 int create256dir(char *prefix) {
  80     char buf[1024];
  81     int j;
  82
  83     for (j = 0; j < 256; j++) {
  84         snprintf(buf,sizeof(buf),"%s%02x",prefix,j);
  85         if (mkdir(buf,0755) == -1) {
  86             redisLog(REDIS_WARNING,"Error creating dir %s for diskstore: %s",
  87                 buf,strerror(errno));
  88             return REDIS_ERR;
  89         }
  90     }
  91     return REDIS_OK;
  92 }
  93
  94 int dsOpen(void) {
  95     struct stat sb;
  96     int retval, j;
  97     char *path = server.ds_path;
  98     char buf[1024];
  99
 100     if ((retval = stat(path,&sb) == -1) && errno != ENOENT) {
 101         redisLog(REDIS_WARNING, "Error opening disk store at %s: %s",
 102                 path, strerror(errno));
 103         return REDIS_ERR;
 104     }
 105
 106     /* Directory already in place. Assume everything is ok. */
 107     if (retval == 0 && S_ISDIR(sb.st_mode)) {
 108         redisLog(REDIS_NOTICE,"Disk store %s exists", path);
 109         return REDIS_OK;
 110     }
 111
 112     /* File exists but it's not a directory */
 113     if (retval == 0 && !S_ISDIR(sb.st_mode)) {
 114         redisLog(REDIS_WARNING,"Disk store at %s is not a directory", path);
 115         return REDIS_ERR;
 116     }
 117
 118     /* New disk store, create the directory structure now, as creating
 119      * them in a lazy way is not a good idea, after very few insertions
 120      * we'll need most of the 65536 directories anyway. */
 121     redisLog(REDIS_NOTICE,"Disk store %s does not exist: creating", path);
 122     if (mkdir(path,0755) == -1) {
 123         redisLog(REDIS_WARNING,"Disk store init failed creating dir %s: %s",
 124             path, strerror(errno));
 125         return REDIS_ERR;
 126     }
 127     /* Create the top level 256 directories */
 128     snprintf(buf,sizeof(buf),"%s/",path);
 129     if (create256dir(buf) == REDIS_ERR) return REDIS_ERR;
 130
 131     /* For every 256 top level dir, create 256 nested dirs */
 132     for (j = 0; j < 256; j++) {
 133         snprintf(buf,sizeof(buf),"%s/%02x/",path,j);
 134         if (create256dir(buf) == REDIS_ERR) return REDIS_ERR;
 135     }
 136     return REDIS_OK;
 137 }
 138
 139 int dsClose(void) {
 140     return REDIS_OK;
 141 }
 142
 143 /* Convert key into full path for this object. Dirty but hopefully
 144  * is fast enough. Returns the length of the returned path. */
 145 int dsKeyToPath(redisDb *db, char *buf, robj *key) {
 146     SHA1_CTX ctx;
 147     unsigned char hash[20];
 148     char hex[40], digits[] = "0123456789abcdef";
 149     int j, l;
 150     char *origbuf = buf;
 151
 152     SHA1Init(&ctx);
 153     SHA1Update(&ctx,key->ptr,sdslen(key->ptr));
 154     SHA1Final(hash,&ctx);
 155
 156     /* Convert the hash into hex format */
 157     for (j = 0; j < 20; j++) {
 158         hex[j*2] = digits[(hash[j]&0xF0)>>4];
 159         hex[(j*2)+1] = digits[hash[j]&0x0F];
 160     }
 161
 162     /* Create the object path. Start with server.ds_path that's the root dir */
 163     l = sdslen(server.ds_path);
 164     memcpy(buf,server.ds_path,l);
 165     buf += l;
 166     *buf++ = '/';
 167
 168     /* Then add xx/yy/ that is the two level directories */
 169     buf[0] = hex[0];
 170     buf[1] = hex[1];
 171     buf[2] = '/';
 172     buf[3] = hex[2];
 173     buf[4] = hex[3];
 174     buf[5] = '/';
 175     buf += 6;
 176
 177     /* Add the database number followed by _ and finall the SHA1 hex */
 178     l = ll2string(buf,64,db->id);
 179     buf += l;
 180     buf[0] = '_';
 181     memcpy(buf+1,hex,40);
 182     buf[41] = '\0';
 183     return (buf-origbuf)+41;
 184 }
 185
 186 int dsSet(redisDb *db, robj *key, robj *val) {
 187     char buf[1024], buf2[1024];
 188     FILE *fp;
 189     int retval, len;
 190
 191     len = dsKeyToPath(db,buf,key);
 192     memcpy(buf2,buf,len);
 193     snprintf(buf2+len,sizeof(buf2)-len,"%ld.%ld",(long)time(NULL),(long)val);
 194     fp = fopen(buf2,"w");
 195     if ((retval = rdbSaveKeyValuePair(fp,db,key,val,time(NULL))) == -1)
 196         return REDIS_ERR;
 197     fclose(fp);
 198     if (retval == 0) {
 199         /* Expired key. Unlink failing not critical */
 200         unlink(buf);
 201         unlink(buf2);
 202     } else {
 203         /* Use rename for atomic updadte of value */
 204         if (rename(buf2,buf) == -1) {
 205             redisLog(REDIS_WARNING,"rename(2) returned an error: %s",
 206                 strerror(errno));
 207             redisPanic("Unrecoverable diskstore error. Exiting.");
 208         }
 209     }
 210     return REDIS_OK;
 211 }
 212
 213 robj *dsGet(redisDb *db, robj *key, time_t *expire) {
 214     char buf[1024];
 215     int type;
 216     time_t expiretime = -1; /* -1 means: no expire */
 217     robj *dskey; /* Key as loaded from disk. */
 218     robj *val;
 219     FILE *fp;
 220
 221     dsKeyToPath(db,buf,key);
 222     fp = fopen(buf,"r");
 223     if (fp == NULL && errno == ENOENT) return NULL; /* No such key */
 224     if (fp == NULL) {
 225         redisLog(REDIS_WARNING,"Disk store failed opening %s: %s",
 226             buf, strerror(errno));
 227         goto readerr;
 228     }
 229
 230     if ((type = rdbLoadType(fp)) == -1) goto readerr;
 231     if (type == REDIS_EXPIRETIME) {
 232         if ((expiretime = rdbLoadTime(fp)) == -1) goto readerr;
 233         /* We read the time so we need to read the object type again */
 234         if ((type = rdbLoadType(fp)) == -1) goto readerr;
 235     }
 236     /* Read key */
 237     if ((dskey = rdbLoadStringObject(fp)) == NULL) goto readerr;
 238     /* Read value */
 239     if ((val = rdbLoadObject(type,fp)) == NULL) goto readerr;
 240     fclose(fp);
 241
 242     /* The key we asked, and the key returned, must be the same */
 243     redisAssert(equalStringObjects(key,dskey));
 244
 245     /* Check if the key already expired */
 246     decrRefCount(dskey);
 247     if (expiretime != -1 && expiretime < time(NULL)) {
 248         decrRefCount(val);
 249         unlink(buf); /* This failing is non critical here */
 250         return NULL;
 251     }
 252
 253     /* Everything ok... */
 254     *expire = expiretime;
 255     return val;
 256
 257 readerr:
 258     redisLog(REDIS_WARNING,"Read error reading reading %s. Corrupted key?",
 259         buf);
 260     redisPanic("Unrecoverable error reading from disk store");
 261     return NULL; /* unreached */
 262 }
 263
 264 int dsDel(redisDb *db, robj *key) {
 265     char buf[1024];
 266
 267     dsKeyToPath(db,buf,key);
 268     if (unlink(buf) == -1) {
 269         if (errno == ENOENT) {
 270             return REDIS_ERR;
 271         } else {
 272             redisLog(REDIS_WARNING,"Disk store can't remove %s: %s",
 273                 buf, strerror(errno));
 274             redisPanic("Unrecoverable Disk store errore. Existing.");
 275             return REDIS_ERR; /* unreached */
 276         }
 277     } else {
 278         return REDIS_OK;
 279     }
 280 }
 281
 282 int dsExists(redisDb *db, robj *key) {
 283     char buf[1024];
 284
 285     dsKeyToPath(db,buf,key);
 286     return access(buf,R_OK) == 0;
 287 }
 288
 289 void dsFlushOneDir(char *path, int dbid) {
 290     DIR *dir;
 291     struct dirent *dp, de;
 292
 293     dir = opendir(path);
 294     if (dir == NULL) {
 295         redisLog(REDIS_WARNING,"Disk store can't open dir %s: %s",
 296             path, strerror(errno));
 297         redisPanic("Unrecoverable Disk store errore. Existing.");
 298     }
 299     while(1) {
 300         char buf[1024];
 301
 302         readdir_r(dir,&de,&dp);
 303         if (dp == NULL) break;
 304         if (dp->d_name[0] == '.') continue;
 305
 306         /* Check if we need to remove this entry accordingly to the
 307          * DB number */
 308         if (dbid != -1) {
 309             char id[64];
 310             char *p = strchr(dp->d_name,'_');
 311             int len = (p - dp->d_name);
 312
 313             redisAssert(p != NULL && len < 64);
 314             memcpy(id,dp->d_name,len);
 315             id[len] = '\0';
 316             if (atoi(id) != dbid) continue; /* skip this file */
 317         }
 318
 319         /* Finally unlink the file */
 320         snprintf(buf,1024,"%s/%s",path,dp->d_name);
 321         if (unlink(buf) == -1) {
 322             redisLog(REDIS_WARNING,
 323                 "Can't unlink %s: %s", buf, strerror(errno));
 324             redisPanic("Unrecoverable Disk store errore. Existing.");
 325         }
 326     }
 327     closedir(dir);
 328 }
 329
 330 void dsFlushDb(int dbid) {
 331     char buf[1024];
 332     int j, i;
 333
 334     redisLog(REDIS_NOTICE,"Flushing diskstore DB (%d)",dbid);
 335     for (j = 0; j < 256; j++) {
 336         for (i = 0; i < 256; i++) {
 337             snprintf(buf,1024,"%s/%02x/%02x",server.ds_path,j,i);
 338             dsFlushOneDir(buf,dbid);
 339         }
 340     }
 341 }