bug 1431 - moxi invokes vbucket_compare()

so that moxi does a better job of reusing pre-existing
downstream connections.

Change-Id: I9f803b062bf6f94e7d9f0a52d3e697826de29a50
Reviewed-on: http://review.northscale.com:8080/651
Reviewed-by: Dustin Sallings <dustin@spy.net>
Tested-by: Dustin Sallings <dustin@spy.net>

cproxy.c

@@ -919,14 +919,30 @@ bool cproxy_check_downstream_config(downstream *d) {
         rv = true;
     } else if (d->config != NULL &&
                d->ptd->config != NULL &&
-               strcmp(d->config,
-                      d->ptd->config) == 0 &&
                cproxy_equal_behaviors(d->behaviors_num,
                                       d->behaviors_arr,
                                       d->ptd->behavior_pool.num,
                                       d->ptd->behavior_pool.arr)) {
-        d->config_ver = d->ptd->config_ver;
-        rv = true;
+        // Parse the proxy/parent's config to see if we can
+        // reuse our existing downstream connections.
+        //
+        mcs_st next;
+
+        int n = init_mcs_st(&next, d->ptd->config);
+        if (n > 0) {
+            if (mcs_stable_update(&d->mst, &next)) {
+                if (settings.verbose > 2) {
+                    fprintf(stderr, "check_downstream_config stable update\n");
+                }
+
+                free(d->config);
+                d->config     = strdup(d->ptd->config);
+                d->config_ver = d->ptd->config_ver;
+                rv = true;
+            }
+
+            mcs_free(&next);
+        }
     }
 
     if (settings.verbose > 2) {

mcs.c

@@ -91,6 +91,34 @@ mcs_server_st *mcs_server_index(mcs_st *ptr, int i) {
     return &ptr->servers[i];
 }
 
+/* Returns true if curr_version could be updated with next_version in
+ * a low-impact stable manner (server-list is the same), allowing the
+ * same connections to be reused.  Or returns false if the delta was
+ * too large for an in-place updating of curr_version with information
+ * from next_version.
+ *
+ * The next_version may be destroyed in this call, and the caller
+ * should afterwards only call mcs_free() on the next_version.
+ */
+bool mcs_stable_update(mcs_st *curr_version, mcs_st *next_version) {
+    bool rv = false;
+
+    VBUCKET_CONFIG_DIFF *diff = vbucket_compare(curr_version->vch, next_version->vch);
+    if (diff != NULL) {
+        if (!diff->sequence_changed) {
+            vbucket_config_destroy(curr_version->vch);
+            curr_version->vch = next_version->vch;
+            next_version->vch = 0;
+
+            rv = true;
+        }
+
+        vbucket_free_diff(diff);
+    }
+
+    return rv;
+}
+
 uint32_t mcs_key_hash(mcs_st *ptr, const char *key, size_t key_length, int *vbucket) {
     int v = vbucket_get_vbucket_by_key(ptr->vch, key, key_length);
     if (vbucket != NULL) {
@@ -277,6 +305,10 @@ mcs_server_st *mcs_server_index(mcs_st *ptr, int i) {
     return &ptr->hosts[i];
 }
 
+bool mcs_stable_update(mcs_st *curr_version, mcs_st *next_version) {
+    return false;
+}
+
 uint32_t mcs_key_hash(mcs_st *ptr, const char *key, size_t key_length, *vbucket) {
     if (vbucket != NULL) {
         *vbucket = -1;

mcs.h

@@ -63,6 +63,8 @@ memcached_return memcached_do(memcached_server_st *ptr,
 mcs_st *mcs_create(mcs_st *ptr, const char *config);
 void    mcs_free(mcs_st *ptr);
 
+bool mcs_stable_update(mcs_st *curr_version, mcs_st *next_version);
+
 uint32_t       mcs_server_count(mcs_st *ptr);
 mcs_return     mcs_server_push(mcs_st *ptr, mcs_server_st *list);
 mcs_server_st *mcs_server_index(mcs_st *ptr, int i);