Fix retain_at_least

Reviewed By: pepeiborra, iamirzhan

Differential Revision: D66097112

fbshipit-source-id: 3ebad2b35b664ab2fe05ad8641a006dbe88b8b53

glean/db/Glean/Database/Config.hs

@@ -158,7 +158,7 @@ data Config = Config
   , cfgEnableRecursion :: Bool
     -- ^ Enable experimental support for recursion
   , cfgFilterAvailableDBs :: [Repo] -> IO [Repo]
-    -- ^ Filter out DBs not currently available in the server tier
+    -- ^ Filter out DBs not currently available on some other server
   , cfgTracer :: Tracer GleanTrace
   , cfgDebug :: DebugFlags
   }
@@ -203,7 +203,7 @@ instance Default Config where
     , cfgDatabaseLogger = Some NullGleanDatabaseLogger
     , cfgBackupBackends = HashMap.fromList [("mock", Backup.Mock.mock)]
     , cfgEnableRecursion = False
-    , cfgFilterAvailableDBs = return
+    , cfgFilterAvailableDBs = const $ return []
     , cfgTracer = mempty
     , cfgDebug = def
     }
@@ -447,7 +447,7 @@ options = do
     , cfgServerLogger = cfgServerLogger def
     , cfgDatabaseLogger = cfgDatabaseLogger def
     , cfgBackupBackends = cfgBackupBackends def
-    , cfgFilterAvailableDBs = return
+    , cfgFilterAvailableDBs = const $ return []
     , cfgTracer = mempty
     , cfgSchemaId = Nothing
     , .. }

glean/db/Glean/Database/Retention.hs

@@ -254,8 +254,16 @@ dbRetentionForRepo ServerConfig.Retention{..} t isAvailableM dbs dbIndex = do
       (ifSet deleteIncompleteIfOlder $ \secs ->
         (not . isComplete) &&& isOlderThan secs)
 
-    -- ensure we have retain_at_least DBs from the available set
-  atLeast <- takeFilterM
+    -- implements retain_at_least
+    atLeast =
+      take retainAtLeast $
+      filter (isComplete &&& hasDependencies) sorted
+
+  -- Ensure we have retain_at_least DBs available somewhere.  This
+  -- prevents us deleting an older DB before the newer one has been
+  -- restored. The isAvailable check ensures that we don't keep an old
+  -- DB on this server when the newer one is on another server.
+  atLeastAvailable <- takeFilterM
     retainAtLeast
     (isComplete &&& hasDependencies &&&> isAvailable)
     -- bound the search since isAvailable is expensive
@@ -265,7 +273,8 @@ dbRetentionForRepo ServerConfig.Retention{..} t isAvailableM dbs dbIndex = do
     -- delete DBs according to the deletion policy, and keep retain_at_most
   let atMost = maybe id take retainAtMost (filter (not . delete) sorted)
 
-  return $ uniqBy (comparing itemRepo) (atLeast ++ atMost)
+  return $ uniqBy (comparing itemRepo) $
+    atLeast ++ atLeastAvailable ++ atMost
 
 missingDependencies :: DbIndex -> Item -> Bool
 missingDependencies dbIndex item = any isNothing (dependencies dbIndex item)