CODEWITHSUNDEEP
phpredisphpredisredis-cluster
sreeraag
sreeraag

Reputation: 523

phpredis Redis cluster connection objects reuse across requests

We use phpredis Library to connect to our 64 node Redis cluster from our serving machines. Though we make use of persistent connections, as php doesn't reuse objects across requests, every request makes a CLUSTER SLOTS call to the Redis Cluster first, and then makes a data fetch. This is proving to be very costly as this increases CPU on both the API and Redis and also increases network usage for meta info (CLUSTER SLOTS) that could otherwise be cached. Basically, we want the Redis cluster connection object to be re-used across multiple requests, in the same php-fpm process. Any suggestions on how to do this?

UPDATE: I tried the following diff in cluster_library.c code but this seems to be causing random runtime exceptions in php.

index 3e532b7..b2cbf16 100644
--- a/cluster_library.c
+++ b/cluster_library.c
@@ -7,6 +7,10 @@
 #include <zend_exceptions.h>

 extern zend_class_entry *redis_cluster_exception_ce;
+int cache_count = 0;
+//Cache the cluster slots value for every n requests/calls, n being 100 for now
+int CACHE_COUNT_VAL = 10;
+clusterReply *permSlots=NULL;

 /* Debugging methods/
 static void cluster_dump_nodes(redisCluster *c) {
@@ -939,7 +943,18 @@ PHP_REDIS_API int cluster_map_keyspace(redisCluster *c TSRMLS_DC) {
         }

         // Parse out cluster nodes.  Flag mapped if we are valid
-        slots = cluster_get_slots(seed TSRMLS_CC);
+ if (permSlots && cache_count <= CACHE_COUNT_VAL) {
+         slots = permSlots;
+         cache_count++;
+ }
+ else {
+         slots = cluster_get_slots(seed TSRMLS_CC);
+ }
+
         if (slots) {
             mapped = !cluster_map_slots(c, slots);
             // Bin anything mapped, if we failed somewhere
@@ -951,8 +966,16 @@ PHP_REDIS_API int cluster_map_keyspace(redisCluster *c TSRMLS_DC) {
         if (mapped) break;
     } ZEND_HASH_FOREACH_END();

+    if((!permSlots && mapped && slots) ||
+             cache_count >= CACHE_COUNT_VAL) {
+ permSlots = slots;
+ cache_count = 0;
+    }
+
     // Clean up slots reply if we got one
-    if(slots) cluster_free_reply(slots, 1);
+    // if(slots) cluster_free_reply(slots, 1);

     // Throw an exception if we couldn't map
     if(!mapped) {

Upvotes: 1

Views: 2574

Answers (1)

Michael Grunder
Michael Grunder

Reputation: 43

Developer of phpredis here. At present this is a limitation/flaw in phpredis as it has to issue a CLUSTER SLOTS command for each new request. As far as I know the only way to avoid this is by pointing phpredis to a proxy like Codis or Corvis but I don't have any personal experience using them.

That being said, I did implement experimental support for this feature in this branch. It uses PHP's persistent_list to cache slot information across requests.

As Redis Cluster adoption appears to be ramping up, I am going to try to get this into the mainline develop branch soon and perhaps into the next stable release!

Cheers, Mike

Upvotes: 4

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