Make sure we're using indexes during rollbacks

Fixes #2083 (comment)
The planner sometimes uses a query similar to

Index Scan using tx_pkey on tx
  Filter: (block_id >= $1)

the filter is not Index Cond, so this ends up in a sequential scan.
The index refers to the primary key and is only used for sorting.
Instead we want to use

Sort (top-N heapsort)
  -> Index Scan using idx_tx_block_id
       Index Cond: (block_id >= $1)

With this change we're forcing a similar plan

Aggregate
  -> Index Scan using idx_tx_block_id
       Index Cond: (block_id >= $1)

making sure we're using the Index Cond and then sorting.

Author: kderme

cardano-db/src/Cardano/Db/Statement/MinIds.hs

@@ -48,20 +48,18 @@ queryMinRefIdStmt ::
   -- | Raw ID decoder (Int64)
   HsqlD.Row Int64 ->
   HsqlStmt.Statement b (Maybe Int64)
-queryMinRefIdStmt fieldName encoder idDecoder =
+queryMinRefIdStmt fieldName encoder _idDecoder =
   HsqlStmt.Statement sql encoder decoder True
   where
     validCol = validateColumn @a fieldName
     sql =
       TextEnc.encodeUtf8 $
         Text.concat
-          [ "SELECT id"
+          [ "SELECT MIN(id)"
           , " FROM " <> tableName (Proxy @a)
           , " WHERE " <> validCol <> " >= $1"
-          , " ORDER BY id ASC"
-          , " LIMIT 1"
           ]
-    decoder = HsqlD.rowMaybe idDecoder
+    decoder = HsqlD.singleRow (HsqlD.column (HsqlD.nullable HsqlD.int8))
 
 queryMinRefId ::
   forall a b.
@@ -92,21 +90,19 @@ queryMinRefIdNullableStmt ::
   -- | Raw ID decoder (Int64)
   HsqlD.Row Int64 ->
   HsqlStmt.Statement b (Maybe Int64)
-queryMinRefIdNullableStmt fieldName encoder idDecoder =
+queryMinRefIdNullableStmt fieldName encoder _idDecoder =
   HsqlStmt.Statement sql encoder decoder True
   where
     validCol = validateColumn @a fieldName
-    decoder = HsqlD.rowMaybe idDecoder
     sql =
       TextEnc.encodeUtf8 $
         Text.concat
-          [ "SELECT id"
+          [ "SELECT MIN(id)"
           , " FROM " <> tableName (Proxy @a)
           , " WHERE " <> validCol <> " IS NOT NULL"
           , " AND " <> validCol <> " >= $1"
-          , " ORDER BY id ASC"
-          , " LIMIT 1"
           ]
+    decoder = HsqlD.singleRow (HsqlD.column (HsqlD.nullable HsqlD.int8))
 
 queryMinRefIdNullable ::
   forall a b.