Disable read ahead in LMDB.

This contributes to not degrading performance too much when the system
memory is almost completely used, by preventing page thrashing due to
the read ahead behaviour of the system.

diff --git a/modules/lmdbbackend/lmdbbackend.cc b/modules/lmdbbackend/lmdbbackend.cc
index d75ec276879d769bf48bc4dc63f8f2ce40b2ea74..164192a8a3ef6711c66cf99a064488725b977a2d 100644 (file)
--- a/modules/lmdbbackend/lmdbbackend.cc
+++ b/modules/lmdbbackend/lmdbbackend.cc
@@ -738,7 +738,7 @@ LMDBBackend::LMDBBackend(const std::string& suffix)
         throw std::runtime_error("Somehow, we are not at schema version 5. Giving up");
       }
 
-      d_tdomains = std::make_shared<tdomains_t>(getMDBEnv(getArg("filename").c_str(), MDB_NOSUBDIR | d_asyncFlag, 0600, mapSize), "domains_v5");
+      d_tdomains = std::make_shared<tdomains_t>(getMDBEnv(getArg("filename").c_str(), MDB_NOSUBDIR | MDB_NORDAHEAD | d_asyncFlag, 0600, mapSize), "domains_v5");
       d_tmeta = std::make_shared<tmeta_t>(d_tdomains->getEnv(), "metadata_v5");
       d_tkdb = std::make_shared<tkdb_t>(d_tdomains->getEnv(), "keydata_v5");
       d_ttsig = std::make_shared<ttsig_t>(d_tdomains->getEnv(), "tsig_v5");
@@ -800,7 +800,7 @@ LMDBBackend::LMDBBackend(const std::string& suffix)
   }
 
   if (!opened) {
-    d_tdomains = std::make_shared<tdomains_t>(getMDBEnv(getArg("filename").c_str(), MDB_NOSUBDIR | d_asyncFlag, 0600, mapSize), "domains_v5");
+    d_tdomains = std::make_shared<tdomains_t>(getMDBEnv(getArg("filename").c_str(), MDB_NOSUBDIR | MDB_NORDAHEAD | d_asyncFlag, 0600, mapSize), "domains_v5");
     d_tmeta = std::make_shared<tmeta_t>(d_tdomains->getEnv(), "metadata_v5");
     d_tkdb = std::make_shared<tkdb_t>(d_tdomains->getEnv(), "keydata_v5");
     d_ttsig = std::make_shared<ttsig_t>(d_tdomains->getEnv(), "tsig_v5");
@@ -1254,7 +1254,7 @@ std::shared_ptr<LMDBBackend::RecordsRWTransaction> LMDBBackend::getRecordsRWTran
   auto& shard = d_trecords[id % s_shards];
   if (!shard.env) {
     shard.env = getMDBEnv((getArg("filename") + "-" + std::to_string(id % s_shards)).c_str(),
-                          MDB_NOSUBDIR | d_asyncFlag, 0600);
+                          MDB_NOSUBDIR | MDB_NORDAHEAD | d_asyncFlag, 0600);
     shard.dbi = shard.env->openDB("records_v5", MDB_CREATE);
   }
   auto ret = std::make_shared<RecordsRWTransaction>(shard.env->getRWTransaction());
@@ -1271,7 +1271,7 @@ std::shared_ptr<LMDBBackend::RecordsROTransaction> LMDBBackend::getRecordsROTran
       throw DBException("attempting to start nested transaction without open parent env");
     }
     shard.env = getMDBEnv((getArg("filename") + "-" + std::to_string(id % s_shards)).c_str(),
-                          MDB_NOSUBDIR | d_asyncFlag, 0600);
+                          MDB_NOSUBDIR | MDB_NORDAHEAD | d_asyncFlag, 0600);
     shard.dbi = shard.env->openDB("records_v5", MDB_CREATE);
   }