Implement consistent hashing algorithm for RedisArray

1 files changed, 81 insertions, 5 deletions

diff --git a/redis_array_impl.c b/redis_array_impl.c
index 6280b4ca..c5d4796c 100644
--- a/redis_array_impl.c
+++ b/redis_array_impl.c
@@ -24,6 +24,7 @@
 #include "SAPI.h"
 #include "ext/standard/url.h"
 #include "ext/standard/crc32.h"
+#include "ext/standard/md5.h"
 
 #define PHPREDIS_INDEX_NAME "__phpredis_array_index__"
 
@@ -173,9 +174,10 @@ RedisArray *ra_load_array(const char *name TSRMLS_DC) {
     zval z_params_connect_timeout;
     zval z_params_read_timeout;
     zval z_params_lazy_connect;
+    zval z_params_consistent;
     RedisArray *ra = NULL;
 
-    zend_bool b_index = 0, b_autorehash = 0, b_pconnect = 0;
+    zend_bool b_index = 0, b_autorehash = 0, b_pconnect = 0, consistent = 0;
     long l_retry_interval = 0;
     zend_bool b_lazy_connect = 0;
     double d_connect_timeout = 0, read_timeout = 0.0;
@@ -312,9 +314,20 @@ RedisArray *ra_load_array(const char *name TSRMLS_DC) {
         }
     }
 
+    /* find consistent option */
+    array_init(&z_params_consistent);
+    if ((iptr = INI_STR("redis.arrays.consistent")) != NULL) {
+        sapi_module.treat_data(PARSE_STRING, estrdup(iptr), &z_params_consistent TSRMLS_CC);
+    }
+    if ((z_data = zend_hash_str_find(Z_ARRVAL(z_params_consistent), name, name_len)) != NULL) {
+        if (Z_TYPE_P(z_data) == IS_STRING && strncmp(Z_STRVAL_P(z_data), "1", 1) == 0) {
+            consistent = 1;
+        }
+    }
+
 
     /* create RedisArray object */
-    ra = ra_make_array(hHosts, &z_fun, &z_dist, hPrev, b_index, b_pconnect, l_retry_interval, b_lazy_connect, d_connect_timeout, read_timeout TSRMLS_CC);
+    ra = ra_make_array(hHosts, &z_fun, &z_dist, hPrev, b_index, b_pconnect, l_retry_interval, b_lazy_connect, d_connect_timeout, read_timeout, consistent TSRMLS_CC);
     if (ra) {
         ra->auto_rehash = b_autorehash;
         if(ra->prev) ra->prev->auto_rehash = b_autorehash;
@@ -332,14 +345,55 @@ RedisArray *ra_load_array(const char *name TSRMLS_DC) {
     zval_dtor(&z_params_connect_timeout);
     zval_dtor(&z_params_read_timeout);
     zval_dtor(&z_params_lazy_connect);
+    zval_dtor(&z_params_consistent);
     zval_dtor(&z_dist);
     zval_dtor(&z_fun);
 
     return ra;
 }
 
+static int
+ra_points_cmp(const void *v1, const void *v2)
+{
+    const ContinuumPoint *p1 = v1, *p2 = v2;
+
+    return p1->value < p2->value ? - 1 : p1->value > p2->value;
+}
+
+static Continuum *
+ra_make_continuum(zend_string **hosts, int nb_hosts)
+{
+    int i, j, k, len, idx = 0;
+    char host[HOST_NAME_MAX];
+    unsigned char digest[16];
+    PHP_MD5_CTX ctx;
+    Continuum *c;
+
+    c = ecalloc(1, sizeof(*c));
+    c->nb_points = nb_hosts * 160; /* 40 hashes, 4 numbers per hash = 160 points per server */
+    c->points = ecalloc(c->nb_points, sizeof(*c->points));
+
+    for (i = 0; i < nb_hosts; ++i) {
+        for (j = 0; j < 40; ++j) {
+            len = snprintf(host, sizeof(host), "%.*s-%u", ZSTR_LEN(hosts[i]), ZSTR_VAL(hosts[i]), j);
+            PHP_MD5Init(&ctx);
+            PHP_MD5Update(&ctx, host, len);
+            PHP_MD5Final(digest, &ctx);
+            for (k = 0; k < 4; ++k) {
+                c->points[idx].index = i;
+                c->points[idx++].value = (digest[3 + k * 4] << 24)
+                    | (digest[2 + k * 4] << 16)
+                    | (digest[1 + k * 4] << 8)
+                    | (digest[k * 4]);
+            }
+        }
+    }
+    qsort(c->points, c->nb_points, sizeof(*c->points), ra_points_cmp);
+    return c;
+}
+
 RedisArray *
-ra_make_array(HashTable *hosts, zval *z_fun, zval *z_dist, HashTable *hosts_prev, zend_bool b_index, zend_bool b_pconnect, long retry_interval, zend_bool b_lazy_connect, double connect_timeout, double read_timeout TSRMLS_DC) {
+ra_make_array(HashTable *hosts, zval *z_fun, zval *z_dist, HashTable *hosts_prev, zend_bool b_index, zend_bool b_pconnect, long retry_interval, zend_bool b_lazy_connect, double connect_timeout, double read_timeout, zend_bool consistent TSRMLS_DC) {
 
     int i, count;
     RedisArray *ra;
@@ -357,6 +411,7 @@ ra_make_array(HashTable *hosts, zval *z_fun, zval *z_dist, HashTable *hosts_prev
     ra->pconnect = b_pconnect;
     ra->connect_timeout = connect_timeout;
     ra->read_timeout = read_timeout;
+    ra->continuum = NULL;
 
     if (ra_load_hosts(ra, hosts, retry_interval, b_lazy_connect TSRMLS_CC) == NULL || !ra->count) {
         for (i = 0; i < ra->count; ++i) {
@@ -368,7 +423,7 @@ ra_make_array(HashTable *hosts, zval *z_fun, zval *z_dist, HashTable *hosts_prev
         efree(ra);
         return NULL;
     }
-    ra->prev = hosts_prev ? ra_make_array(hosts_prev, z_fun, z_dist, NULL, b_index, b_pconnect, retry_interval, b_lazy_connect, connect_timeout, read_timeout TSRMLS_CC) : NULL;
+    ra->prev = hosts_prev ? ra_make_array(hosts_prev, z_fun, z_dist, NULL, b_index, b_pconnect, retry_interval, b_lazy_connect, connect_timeout, read_timeout, consistent TSRMLS_CC) : NULL;
 
     /* init array data structures */
     ra_init_function_table(ra);
@@ -377,6 +432,11 @@ ra_make_array(HashTable *hosts, zval *z_fun, zval *z_dist, HashTable *hosts_prev
     ZVAL_ZVAL(&ra->z_fun, z_fun, 1, 0);
     ZVAL_ZVAL(&ra->z_dist, z_dist, 1, 0);
 
+    /* init continuum */
+    if (consistent) {
+        ra->continuum = ra_make_continuum(ra->hosts, ra->count);
+    }
+
     return ra;
 }
 
@@ -480,7 +540,23 @@ ra_find_node(RedisArray *ra, const char *key, int key_len, int *out_pos TSRMLS_D
         }
 
         /* get position on ring */
-        pos = (int)((ret ^ 0xffffffff) * ra->count / 0xffffffff);
+        if (ra->continuum) {
+            int left = 0, right = ra->continuum->nb_points;
+            while (left < right) {
+                i = (int)((left + right) / 2);
+                if (ra->continuum->points[i].value < ret) {
+                    left = i + 1;
+                } else {
+                    right = i;
+                }
+            }
+            if (right == ra->continuum->nb_points) {
+                right = 0;
+            }
+            pos = ra->continuum->points[right].index;
+        } else {
+            pos = (int)((ret ^ 0xffffffff) * ra->count / 0xffffffff);
+        }
     } else {
         pos = ra_call_distributor(ra, key, key_len TSRMLS_CC);
         if (pos < 0 || pos >= ra->count) {