mon: compact PaxosService prefix on trim

Each time we trim a PaxosService, have leveldb compact so that the
space from removed states is reclaimed.

This is probably not optimal if leveldb's heuristics are doing the right
thing, but it currently appears as if they are not.

Signed-off-by: Sage Weil <sage@inktank.com>

2 files changed, 5 insertions, 0 deletions

diff --git a/src/common/config_opts.h b/src/common/config_opts.h
index c8e634f46ac..d78a7cc9d8a 100644
--- a/src/common/config_opts.h
+++ b/src/common/config_opts.h
@@ -126,6 +126,7 @@ OPTION(mon_initial_members, OPT_STR, "")    // list of initial cluster mon ids;
 OPTION(mon_sync_fs_threshold, OPT_INT, 5)   // sync() when writing this many objects; 0 to disable.
 OPTION(mon_compact_on_start, OPT_BOOL, false)  // compact leveldb on ceph-mon start
 OPTION(mon_compact_on_bootstrap, OPT_BOOL, false)  // trigger leveldb compaction on bootstrap
+OPTION(mon_compact_on_trim, OPT_BOOL, false)       // compact (a prefix) when we trim old states
 OPTION(mon_tick_interval, OPT_INT, 5)
 OPTION(mon_subscribe_interval, OPT_DOUBLE, 300)
 OPTION(mon_osd_laggy_halflife, OPT_INT, 60*60)        // (seconds) how quickly our laggy estimations decay
diff --git a/src/mon/PaxosService.cc b/src/mon/PaxosService.cc
index d02cb1d7ab5..647980a9342 100644
--- a/src/mon/PaxosService.cc
+++ b/src/mon/PaxosService.cc
@@ -318,6 +318,10 @@ void PaxosService::trim(MonitorDBStore::Transaction *t,
       t->erase(get_service_name(), full_key);
     }
   }
+  if (g_conf->mon_compact_on_trim) {
+    dout(20) << " compacting prefix " << get_service_name() << dendl;
+    t->compact_prefix(get_service_name());
+  }
 }
 
 void PaxosService::encode_trim(MonitorDBStore::Transaction *t)