fix: Performance and high memory usage of relation hint calculation

* Calculation of hint message when requested relation is not present in schema cache requires creation of a FuzzySet (to use fuzzy search to find candidate tables). For schemas with many tables it is costly.
This patch introduces dbTablesFuzzyIndex in SchemaCache to memoize the FuzzySet creation.

* Additionally, because of FuzzySet large memory requirements, this patch introduces a limit of 500 relations per schema, above which FuzzySet is not created and hint calculation disabled.

src/PostgREST/Error.hs

@@ -3,6 +3,7 @@ Module      : PostgREST.Error
 Description : PostgREST error HTTP responses
 -}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# LANGUAGE NamedFieldPuns  #-}
 {-# LANGUAGE RecordWildCards #-}
 
 module PostgREST.Error
@@ -41,6 +42,7 @@ import Network.HTTP.Types.Header (Header)
 import           PostgREST.MediaType (MediaType (..))
 import qualified PostgREST.MediaType as MediaType
 
+import PostgREST.SchemaCache              (SchemaCache (SchemaCache, dbTablesFuzzyIndex))
 import PostgREST.SchemaCache.Identifiers  (QualifiedIdentifier (..),
                                            Schema)
 import PostgREST.SchemaCache.Relationship (Cardinality (..),
@@ -49,10 +51,8 @@ import PostgREST.SchemaCache.Relationship (Cardinality (..),
                                            RelationshipsMap)
 import PostgREST.SchemaCache.Routine      (Routine (..),
                                            RoutineParam (..))
-import PostgREST.SchemaCache.Table        (Table (..))
 import Protolude
 
-
 class (ErrorBody a, JSON.ToJSON a) => PgrstError a where
   status   :: a -> HTTP.Status
   headers  :: a -> [Header]
@@ -250,7 +250,7 @@ data SchemaCacheError
   | NoRelBetween Text Text (Maybe Text) Text RelationshipsMap
   | NoRpc Text Text [Text] MediaType Bool [QualifiedIdentifier] [Routine]
   | ColumnNotFound Text Text
-  | TableNotFound Text Text [Table]
+  | TableNotFound Text Text SchemaCache
   deriving Show
 
 instance PgrstError SchemaCacheError where
@@ -313,7 +313,7 @@ instance ErrorBody SchemaCacheError where
       where
         onlySingleParams = isInvPost && contentType `elem` [MTTextPlain, MTTextXML, MTOctetStream]
   hint (AmbiguousRpc _)      = Just "Try renaming the parameters or the function itself in the database so function overloading can be resolved"
-  hint (TableNotFound schemaName relName tbls) = JSON.String <$> tableNotFoundHint schemaName relName tbls
+  hint (TableNotFound schemaName relName schemaCache) = JSON.String <$> tableNotFoundHint schemaName relName schemaCache
 
   hint _ = Nothing
 
@@ -428,13 +428,11 @@ noRpcHint schema procName params allProcs overloadedProcs =
 
 -- |
 -- Do a fuzzy search in all tables in the same schema and return closest result
-tableNotFoundHint :: Text -> Text -> [Table] -> Maybe Text
-tableNotFoundHint schema tblName tblList
+tableNotFoundHint :: Text -> Text -> SchemaCache -> Maybe Text
+tableNotFoundHint schema tblName SchemaCache{dbTablesFuzzyIndex}
   = fmap (\tbl -> "Perhaps you meant the table '" <> schema <> "." <> tbl <> "'") perhapsTable
     where
-      perhapsTable = Fuzzy.getOne fuzzyTableSet tblName
-      fuzzyTableSet = Fuzzy.fromList [ tableName tbl | tbl <- tblList, tableSchema tbl == schema]
-
+      perhapsTable = (`Fuzzy.getOne` tblName) =<< HM.lookup schema dbTablesFuzzyIndex
 
 compressedRel :: Relationship -> JSON.Value
 -- An ambiguousness error cannot happen for computed relationships TODO refactor so this mempty is not needed