graphql: Use the correct setting for number of LfuCache shards

This also makes it possible to turn the LfuCache off by setting
GRAPH_QUERY_LFU_CACHE_SHARDS to 0

graph/src/env/graphql.rs

@@ -31,7 +31,7 @@ pub struct EnvVarsGraphQl {
     pub query_block_cache_shards: u8,
     /// Set by the environment variable `GRAPH_QUERY_LFU_CACHE_SHARDS`. The
     /// default value is set to whatever `GRAPH_QUERY_BLOCK_CACHE_SHARDS` is set
-    /// to.
+    /// to. Set to 0 to disable this cache.
     pub query_lfu_cache_shards: u8,
     /// How many blocks per network should be kept in the query cache. When the
     /// limit is reached, older blocks are evicted. This should be kept small

graphql/src/execution/execution.rs

@@ -386,11 +386,11 @@ pub(crate) async fn execute_root_selection_set<R: Resolver>(
 
         if inserted {
             ctx.cache_status.store(CacheStatus::Insert);
-        } else {
+        } else if QUERY_LFU_CACHE.len() > 0 {
             // Results that are too old for the QUERY_BLOCK_CACHE go into the QUERY_LFU_CACHE
+            let shard = (key[0] as usize) % QUERY_LFU_CACHE.len();
             let mut cache = QUERY_LFU_CACHE[shard].lock(&ctx.logger);
-            let max_mem = ENV_VARS.graphql.query_cache_max_mem
-                / (ENV_VARS.graphql.query_block_cache_shards as usize);
+            let max_mem = ENV_VARS.graphql.query_cache_max_mem / QUERY_LFU_CACHE.len();
             cache.evict_with_period(max_mem, ENV_VARS.graphql.query_cache_stale_period);
             cache.insert(
                 key,