Allow to truely disable the RAM node cache

When -C 0 is given, none of the management structures of
node caches will be created, saving another 600 MB of memory.

Only allow when using slim mode. Advisable to be used only
in conjunction with flat node storage.

Author: lonvia

node-ram-cache.cpp

@@ -316,6 +316,9 @@ node_ram_cache::node_ram_cache(int strategy, int cacheSizeMB)
   cacheSize((int64_t)cacheSizeMB * 1024 * 1024), storedNodes(0), totalNodes(0),
   nodesCacheHits(0), nodesCacheLookups(0), warn_node_order(0)
 {
+    if (cacheSize == 0)
+        return;
+
     blockCache = 0;
     blockCachePos = 0;
     /* How much we can fit, and make sure it's odd */
@@ -388,6 +391,9 @@ node_ram_cache::node_ram_cache(int strategy, int cacheSizeMB)
 
 node_ram_cache::~node_ram_cache()
 {
+    if (cacheSize == 0)
+        return;
+
     fprintf(stderr, "node cache: stored: %" PRIdOSMID
                     "(%.2f%%), storage efficiency: %.2f%% (dense blocks: %i, "
                     "sparse nodes: %" PRId64 "), hit rate: %.2f%%\n",
@@ -417,6 +423,9 @@ node_ram_cache::~node_ram_cache()
 
 void node_ram_cache::set(osmid_t id, const osmium::Location &coord)
 {
+    if (cacheSize == 0)
+        return;
+
     if ((id > 0 && id >> BLOCK_SHIFT >> 32) ||
         (id < 0 && ~id >> BLOCK_SHIFT >> 32)) {
         fprintf(stderr, "\nAbsolute node IDs must not be larger than %" PRId64
@@ -448,6 +457,9 @@ osmium::Location node_ram_cache::get(osmid_t id)
 {
     osmium::Location coord;
 
+    if (cacheSize == 0)
+        return coord;
+
     if (allocStrategy & ALLOC_DENSE) {
         coord = get_dense(id);
     }

options.cpp

@@ -592,7 +592,14 @@ void options_t::check_options()
     }
 
     if (cache == 0) {
-        fprintf(stderr, "WARNING: ram cache is disabled. This will likely slow down processing a lot.\n\n");
+        if (!slim) {
+            throw std::runtime_error(
+                "Ram node cache can only be disable in slim mode.\n");
+        }
+        if (!flat_node_cache_enabled) {
+            fprintf(stderr, "WARNING: ram cache is disabled. This will likely "
+                            "slow down processing a lot.\n\n");
+        }
     }
 
     if (num_procs < 1) {