/* Memory layout of a zipmap, for the map "foo" => "bar", "hello" => "world":
*
- * <status><len>"foo"<len><free>"bar"<len>"hello"<len><free>"world"
+ * <zmlen><len>"foo"<len><free>"bar"<len>"hello"<len><free>"world"
*
- * <status> 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.
+ * <zmlen> 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.
*
* <len> is the length of the following string (key or value).
* <len> lengths are encoded in a single value or in a 5 bytes value.
* or even in order to add a key/value pair if it fits.
*
* <free> 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 <len> (coded as already
- * specified). The length includes the 254 bytes in the count and the
- * space taken by the <len> 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.
*/
#include <assert.h>
#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 <free> 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
unsigned char *zipmapNew(void) {
unsigned char *zm = zmalloc(2);
- zm[0] = 0; /* Status */
+ zm[0] = 0; /* Length */
zm[1] = ZIPMAP_END;
return zm;
}
*
* 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. */
+ * 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 l,llen;
while(*p != ZIPMAP_END) {
unsigned char free;
/* Match or skip the key */
l = zipmapDecodeLength(p);
- if (k == NULL && l == klen && !memcmp(p+1,key,l)) {
+ llen = zipmapEncodeLength(NULL,l);
+ if (k == NULL && l == klen && !memcmp(p+llen,key,l)) {
/* Only return when the user doesn't care
* for the total length of the zipmap. */
if (totlen != NULL) {
return p;
}
}
- p += zipmapEncodeLength(NULL,l) + l;
+ p += llen+l;
/* Skip the value as well */
l = zipmapDecodeLength(p);
p += zipmapEncodeLength(NULL,l);
/* Return the total amount used by a key (encoded length + payload) */
static unsigned int zipmapRawKeyLength(unsigned char *p) {
unsigned int l = zipmapDecodeLength(p);
-
return zipmapEncodeLength(NULL,l) + l;
}
* free space if any). */
static unsigned int zipmapRawEntryLength(unsigned char *p) {
unsigned int l = zipmapRawKeyLength(p);
-
return l + zipmapRawValueLength(p+l);
}
* 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 zmlen;
+ unsigned int zmlen, offset;
unsigned int freelen, reqlen = zipmapRequiredLength(klen,vlen);
unsigned int empty, vempty;
unsigned char *p;
zm = zipmapResize(zm, zmlen+reqlen);
p = zm+zmlen-1;
zmlen = zmlen+reqlen;
- } else {
- unsigned char *b = p;
+ /* 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) {
- /* Move remaining entries to the current position, so this
- * pair can be appended. Note: the +1 in memmove is caused
- * by the end-of-zipmap byte. */
- memmove(p, p+freelen, zmlen-((p-zm)+freelen+1));
+ /* 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+zmlen-1-freelen;
- zmlen = zmlen-1-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) {
- memmove(p+reqlen, p+freelen, zmlen-((p-zm)+freelen+1));
+ /* First, move the tail <empty> bytes to the front, then resize
+ * the zipmap to be <empty> 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;
} else {
vempty = empty;
/* 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 int zmlen;
+ 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]--;
+
if (deleted) *deleted = 1;
} else {
if (deleted) *deleted = 0;
* }
*/
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;
/* 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;
}
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;
zm = zipmapSet(zm,(unsigned char*) "surname",7, (unsigned char*) "foo",3,NULL);
zm = zipmapSet(zm,(unsigned char*) "age",3, (unsigned char*) "foo",3,NULL);
zipmapRepr(zm);
- exit(1);
zm = zipmapSet(zm,(unsigned char*) "hello",5, (unsigned char*) "world!",6,NULL);
zm = zipmapSet(zm,(unsigned char*) "foo",3, (unsigned char*) "bar",3,NULL);
zipmapRepr(zm);
zm = zipmapDel(zm,(unsigned char*) "new",3,NULL);
zipmapRepr(zm);
+
+ printf("\nLook up large key:\n");
+ {
+ unsigned char buf[512];
+ unsigned char *value;
+ unsigned int vlen, i;
+ for (i = 0; i < 512; i++) buf[i] = 'a';
+
+ zm = zipmapSet(zm,buf,512,(unsigned char*) "long",4,NULL);
+ if (zipmapGet(zm,buf,512,&value,&vlen)) {
+ printf(" <long key> is associated to the %d bytes value: %.*s\n",
+ vlen, vlen, value);
+ }
+ }
+
printf("\nPerform a direct lookup:\n");
{
unsigned char *value;
projects / redis.git / blobdiff