X-Git-Url: https://git.saurik.com/redis.git/blobdiff_plain/c1d57a106345a811c91a0bf1b6fff42ccbae61a3..723240057a996a64516b10779f754ae26a91d0cd:/zipmap.c diff --git a/zipmap.c b/zipmap.c index 5f024dfa..6c13f806 100644 --- a/zipmap.c +++ b/zipmap.c @@ -42,10 +42,11 @@ /* Memory layout of a zipmap, for the map "foo" => "bar", "hello" => "world": * - * "foo""bar""hello""world" + * "foo""bar""hello""world" * - * is 1 byte status. Currently only 1 bit is used: if the least - * significant bit is set, it means the zipmap needs to be defragmented. + * is 1 byte length that holds the current size of the zipmap. + * When the zipmap length is greater than or equal to 254, this value + * is not used and the zipmap needs to be traversed to find out the length. * * is the length of the following string (key or value). * lengths are encoded in a single value or in a 5 bytes value. @@ -62,22 +63,15 @@ * or even in order to add a key/value pair if it fits. * * is always an unsigned 8 bit number, because if after an - * update operation there are more than a few free bytes, they'll be converted - * into empty space prefixed by the special value 254. + * update operation there are more than a few free bytes, the zipmap will be + * reallocated to make sure it is as small as possible. * * The most compact representation of the above two elements hash is actually: * - * "\x00\x03foo\x03\x00bar\x05hello\x05\x00world\xff" + * "\x02\x03foo\x03\x00bar\x05hello\x05\x00world\xff" * - * Empty space is marked using a 254 bytes + a (coded as already - * specified). The length includes the 254 bytes in the count and the - * space taken by the field. So for instance removing the "foo" key - * from the zipmap above will lead to the following representation: - * - * "\x00\xfd\x10........\x05hello\x05\x00world\xff" - * - * Note that because empty space, keys, values, are all prefixed length - * "objects", the lookup will take O(N) where N is the numeber of elements + * Note that because keys and values are prefixed length "objects", + * the lookup will take O(N) where N is the number of elements * in the zipmap and *not* the number of bytes needed to represent the zipmap. * This lowers the constant times considerably. */ @@ -87,15 +81,12 @@ #include #include "zmalloc.h" -#define ZIPMAP_BIGLEN 253 -#define ZIPMAP_EMPTY 254 +#define ZIPMAP_BIGLEN 254 #define ZIPMAP_END 255 -#define ZIPMAP_STATUS_FRAGMENTED 1 - /* The following defines the max value for the field described in the * comments above, that is, the max number of trailing bytes in a value. */ -#define ZIPMAP_VALUE_MAX_FREE 5 +#define ZIPMAP_VALUE_MAX_FREE 4 /* The following macro returns the number of bytes needed to encode the length * for the integer value _l, that is, 1 byte for lengths < ZIPMAP_BIGLEN and @@ -106,7 +97,7 @@ unsigned char *zipmapNew(void) { unsigned char *zm = zmalloc(2); - zm[0] = 0; /* Status */ + zm[0] = 0; /* Length */ zm[1] = ZIPMAP_END; return zm; } @@ -116,7 +107,7 @@ static unsigned int zipmapDecodeLength(unsigned char *p) { unsigned int len = *p; if (len < ZIPMAP_BIGLEN) return len; - memcpy(&len,p,sizeof(unsigned int)); + memcpy(&len,p+1,sizeof(unsigned int)); return len; } @@ -142,50 +133,34 @@ static unsigned int zipmapEncodeLength(unsigned char *p, unsigned int len) { * * If NULL is returned, and totlen is not NULL, it is set to the entire * size of the zimap, so that the calling function will be able to - * reallocate the original zipmap to make room for more entries. - * - * If NULL is returned, and freeoff and freelen are not NULL, they are set - * to the offset of the first empty space that can hold '*freelen' bytes - * (freelen is an integer pointer used both to signal the required length - * and to get the reply from the function). If there is not a suitable - * free space block to hold the requested bytes, *freelen is set to 0. */ -static unsigned char *zipmapLookupRaw(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned int *totlen, unsigned int *freeoff, unsigned int *freelen) { - unsigned char *p = zm+1; + * reallocate the original zipmap to make room for more entries. */ +static unsigned char *zipmapLookupRaw(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned int *totlen) { + unsigned char *p = zm+1, *k = NULL; unsigned int l; - unsigned int reqfreelen = 0; /* initialized just to prevent warning */ - if (freelen) { - reqfreelen = *freelen; - *freelen = 0; - assert(reqfreelen != 0); - } while(*p != ZIPMAP_END) { - if (*p == ZIPMAP_EMPTY) { - l = zipmapDecodeLength(p+1); - /* if the user want a free space report, and this space is - * enough, and we did't already found a suitable space... */ - if (freelen && l >= reqfreelen && *freelen == 0) { - *freelen = l; - *freeoff = p-zm; + unsigned char free; + + /* Match or skip the key */ + l = zipmapDecodeLength(p); + if (k == NULL && l == klen && !memcmp(p+1,key,l)) { + /* Only return when the user doesn't care + * for the total length of the zipmap. */ + if (totlen != NULL) { + k = p; + } else { + return p; } - p += l; - zm[0] |= ZIPMAP_STATUS_FRAGMENTED; - } else { - unsigned char free; - - /* Match or skip the key */ - l = zipmapDecodeLength(p); - if (l == klen && !memcmp(p+1,key,l)) return p; - p += zipmapEncodeLength(NULL,l) + l; - /* Skip the value as well */ - l = zipmapDecodeLength(p); - p += zipmapEncodeLength(NULL,l); - free = p[0]; - p += l+1+free; /* +1 to skip the free byte */ } + p += zipmapEncodeLength(NULL,l) + l; + /* Skip the value as well */ + l = zipmapDecodeLength(p); + p += zipmapEncodeLength(NULL,l); + free = p[0]; + p += l+1+free; /* +1 to skip the free byte */ } if (totlen != NULL) *totlen = (unsigned int)(p-zm)+1; - return NULL; + return k; } static unsigned long zipmapRequiredLength(unsigned int klen, unsigned int vlen) { @@ -220,64 +195,70 @@ static unsigned int zipmapRawValueLength(unsigned char *p) { * free space if any). */ static unsigned int zipmapRawEntryLength(unsigned char *p) { unsigned int l = zipmapRawKeyLength(p); - return l + zipmapRawValueLength(p+l); } +static inline unsigned char *zipmapResize(unsigned char *zm, unsigned int len) { + zm = zrealloc(zm, len); + zm[len-1] = ZIPMAP_END; + return zm; +} + /* Set key to value, creating the key if it does not already exist. * If 'update' is not NULL, *update is set to 1 if the key was * already preset, otherwise to 0. */ unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char *val, unsigned int vlen, int *update) { - unsigned int oldlen = 0, freeoff = 0, freelen; - unsigned int reqlen = zipmapRequiredLength(klen,vlen); + unsigned int zmlen, offset; + unsigned int freelen, reqlen = zipmapRequiredLength(klen,vlen); unsigned int empty, vempty; unsigned char *p; freelen = reqlen; if (update) *update = 0; - p = zipmapLookupRaw(zm,key,klen,&oldlen,&freeoff,&freelen); - if (p == NULL && freelen == 0) { - /* Key not found, and not space for the new key. Enlarge */ - zm = zrealloc(zm,oldlen+reqlen); - p = zm+oldlen-1; - zm[oldlen+reqlen-1] = ZIPMAP_END; - freelen = reqlen; - } else if (p == NULL) { - /* Key not found, but there is enough free space. */ - p = zm+freeoff; - /* note: freelen is already set in this case */ - } else { - unsigned char *b = p; + p = zipmapLookupRaw(zm,key,klen,&zmlen); + if (p == NULL) { + /* Key not found: enlarge */ + zm = zipmapResize(zm, zmlen+reqlen); + p = zm+zmlen-1; + zmlen = zmlen+reqlen; + /* Increase zipmap length (this is an insert) */ + if (zm[0] < ZIPMAP_BIGLEN) zm[0]++; + } else { /* Key found. Is there enough space for the new value? */ /* Compute the total length: */ if (update) *update = 1; - freelen = zipmapRawKeyLength(b); - b += freelen; - freelen += zipmapRawValueLength(b); + freelen = zipmapRawEntryLength(p); if (freelen < reqlen) { - /* Mark this entry as free and recurse */ - p[0] = ZIPMAP_EMPTY; - zipmapEncodeLength(p+1,freelen); - zm[0] |= ZIPMAP_STATUS_FRAGMENTED; - return zipmapSet(zm,key,klen,val,vlen,NULL); + /* Store the offset of this key within the current zipmap, so + * it can be resized. Then, move the tail backwards so this + * pair fits at the current position. */ + offset = p-zm; + zm = zipmapResize(zm, zmlen-freelen+reqlen); + p = zm+offset; + + /* The +1 in the number of bytes to be moved is caused by the + * end-of-zipmap byte. Note: the *original* zmlen is used. */ + memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1)); + zmlen = zmlen-freelen+reqlen; + freelen = reqlen; } } - /* Ok we have a suitable block where to write the new key/value - * entry. */ + /* We now have a suitable block where the key/value entry can + * be written. If there is too much free space, move the tail + * of the zipmap a few bytes to the front and shrink the zipmap, + * as we want zipmaps to be very space efficient. */ empty = freelen-reqlen; - /* If there is too much free space mark it as a free block instead - * of adding it as trailing empty space for the value, as we want - * zipmaps to be very space efficient. */ - if (empty > ZIPMAP_VALUE_MAX_FREE) { - unsigned char *e; - - e = p+reqlen; - e[0] = ZIPMAP_EMPTY; - zipmapEncodeLength(e+1,empty); + if (empty >= ZIPMAP_VALUE_MAX_FREE) { + /* First, move the tail bytes to the front, then resize + * the zipmap to be bytes smaller. */ + offset = p-zm; + memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1)); + zmlen -= empty; + zm = zipmapResize(zm, zmlen); + p = zm+offset; vempty = 0; - zm[0] |= ZIPMAP_STATUS_FRAGMENTED; } else { vempty = empty; } @@ -297,13 +278,16 @@ unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int kle /* Remove the specified key. If 'deleted' is not NULL the pointed integer is * set to 0 if the key was not found, to 1 if it was found and deleted. */ unsigned char *zipmapDel(unsigned char *zm, unsigned char *key, unsigned int klen, int *deleted) { - unsigned char *p = zipmapLookupRaw(zm,key,klen,NULL,NULL,NULL); + unsigned int zmlen, freelen; + unsigned char *p = zipmapLookupRaw(zm,key,klen,&zmlen); if (p) { - unsigned int freelen = zipmapRawEntryLength(p); + freelen = zipmapRawEntryLength(p); + memmove(p, p+freelen, zmlen-((p-zm)+freelen+1)); + zm = zipmapResize(zm, zmlen-freelen); + + /* Decrease zipmap length */ + if (zm[0] < ZIPMAP_BIGLEN) zm[0]--; - p[0] = ZIPMAP_EMPTY; - zipmapEncodeLength(p+1,freelen); - zm[0] |= ZIPMAP_STATUS_FRAGMENTED; if (deleted) *deleted = 1; } else { if (deleted) *deleted = 0; @@ -328,8 +312,6 @@ unsigned char *zipmapRewind(unsigned char *zm) { * } */ unsigned char *zipmapNext(unsigned char *zm, unsigned char **key, unsigned int *klen, unsigned char **value, unsigned int *vlen) { - while(zm[0] == ZIPMAP_EMPTY) - zm += zipmapDecodeLength(zm+1); if (zm[0] == ZIPMAP_END) return NULL; if (key) { *key = zm; @@ -351,7 +333,7 @@ unsigned char *zipmapNext(unsigned char *zm, unsigned char **key, unsigned int * int zipmapGet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char **value, unsigned int *vlen) { unsigned char *p; - if ((p = zipmapLookupRaw(zm,key,klen,NULL,NULL,NULL)) == NULL) return 0; + if ((p = zipmapLookupRaw(zm,key,klen,NULL)) == NULL) return 0; p += zipmapRawKeyLength(p); *vlen = zipmapDecodeLength(p); *value = p + ZIPMAP_LEN_BYTES(*vlen) + 1; @@ -360,15 +342,21 @@ int zipmapGet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned /* Return 1 if the key exists, otherwise 0 is returned. */ int zipmapExists(unsigned char *zm, unsigned char *key, unsigned int klen) { - return zipmapLookupRaw(zm,key,klen,NULL,NULL,NULL) != NULL; + return zipmapLookupRaw(zm,key,klen,NULL) != NULL; } /* Return the number of entries inside a zipmap */ unsigned int zipmapLen(unsigned char *zm) { - unsigned char *p = zipmapRewind(zm); unsigned int len = 0; + if (zm[0] < ZIPMAP_BIGLEN) { + len = zm[0]; + } else { + unsigned char *p = zipmapRewind(zm); + while((p = zipmapNext(p,NULL,NULL,NULL,NULL)) != NULL) len++; - while((p = zipmapNext(p,NULL,NULL,NULL,NULL)) != NULL) len++; + /* Re-store length if small enough */ + if (len < ZIPMAP_BIGLEN) zm[0] = len; + } return len; } @@ -380,10 +368,6 @@ void zipmapRepr(unsigned char *p) { if (p[0] == ZIPMAP_END) { printf("{end}"); break; - } else if (p[0] == ZIPMAP_EMPTY) { - l = zipmapDecodeLength(p+1); - printf("{%u empty block}", l); - p += l; } else { unsigned char e;