From: Miod Vallat <miod.vallat@open-xchange.com>
Date: Wed, 12 Feb 2025 11:45:27 +0000 (+0100)
Subject: Disable read ahead in LMDB.
X-Git-Tag: dnsdist-2.0.0-alpha1~100^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2eaf1e25e42dac6a9d2d62030d220a66fe3c8845;p=thirdparty%2Fpdns.git

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 d75ec27687..164192a8a3 100644
--- 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);
   }