tracker/trunk/0001-libtracker-data-Workaround-SQLite-3.35.x-bug.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Carlos Garnacho <carlosg@gnome.org>
   3 Date: Sun, 21 Mar 2021 17:38:48 +0100
   4 Subject: [PATCH] libtracker-data: Workaround SQLite 3.35.x bug
   5
   6 The optimization for UNION ALLs inside JOINs had another unexpected
   7 victim:
   8
   9   SELECT * { GRAPH ?g { ?a ... OPTIONAL { ?a ... } } }
  10
  11 Does now break when matching the graph between both sides of the
  12 LEFT JOIN caused by OPTIONAL, making all other values coming from
  13 the right hand side come back empty. Make it sure this specific case
  14 is ineligible for query flattening optimizations by adding a LIMIT
  15 clause on the right hand side of the LEFT JOIN. This brings back
  16 correct over fast.
  17
  18 This workaround should be revisited when a SQLite fix is available.
  19 ---
  20  src/libtracker-data/tracker-sparql.c | 22 +++++++++++++++++++++-
  21  1 file changed, 21 insertions(+), 1 deletion(-)
  22
  23 diff --git a/src/libtracker-data/tracker-sparql.c b/src/libtracker-data/tracker-sparql.c
  24 index e36d2341e684..60e50c611ab8 100644
  25 --- a/src/libtracker-data/tracker-sparql.c
  26 +++ b/src/libtracker-data/tracker-sparql.c
  27 @@ -3170,8 +3170,28 @@ translate_OptionalGraphPattern (TrackerSparql  *sparql,
  28
  29         _call_rule (sparql, NAMED_RULE_GroupGraphPattern, error);
  30
  31 -       if (do_join)
  32 +       if (do_join) {
  33 +               /* FIXME: This is a workaround for SQLite 3.35.x, where
  34 +                * the optimization on UNION ALLs inside JOINs (Point 8c in
  35 +                * the 3.35.0 release notes) break in this very specific
  36 +                * case:
  37 +                *
  38 +                *   SELECT * { GRAPH ?g { ?a ... OPTIONAL { ?a ... } } }
  39 +                *
  40 +                * This is a workaround to make this one case ineligible
  41 +                * for query flattening optimizations, specifically make
  42 +                * it fall through case 8 in the list at
  43 +                * https://sqlite.org/optoverview.html#flattening,
  44 +                * "The subquery does not use LIMIT or the outer query is not
  45 +                * a join.", we will now meet both here.
  46 +                *
  47 +                * This should be evaluated again in future SQLite versions.
  48 +                */
  49 +               if (tracker_token_get_variable (&sparql->current_state.graph))
  50 +                       _append_string (sparql, "LIMIT -1 ");
  51 +
  52                 _append_string (sparql, ") ");
  53 +       }
  54
  55         return TRUE;
  56  }