From 4677d81032da59818f81d0bed7538c034a110fe5 Mon Sep 17 00:00:00 2001
From: Carlos Garnacho <carlosg@gnome.org>
Date: Sat, 7 Nov 2020 22:59:13 +0100
Subject: libtracker-data: Optimize easily catchable idempotent deletes

Operations like "DELETE WHERE { <urn> ... }" can be tiptoed if we know
that <urn> is not a known resource yet, avoiding it's full evaluation.

These operations are a fairly common result from using TrackerResource
(e.g. ensuring multivalued properties are in a clean slate), they are
common enough that it's prominent in first-index tracker-miner-fs-3
perf records, e.g.:

  15.79%     0.01%  pool-tracker-mi  libtracker-sparql-3.0.so.0.100.0  [.] translate_DeleteWhere

With this change in place, the same situation becomes:

  3.70%     0.07%  pool-tracker-mi  libtracker-sparql-3.0.so.0.100.0  [.] translate_DeleteWhere
---
 src/libtracker-data/tracker-sparql.c | 64 ++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/src/libtracker-data/tracker-sparql.c b/src/libtracker-data/tracker-sparql.c
index 06c4bb45c..6a914f255 100644
--- a/src/libtracker-data/tracker-sparql.c
+++ b/src/libtracker-data/tracker-sparql.c
@@ -4500,6 +4500,66 @@ iterate_solution (TrackerSparql      *sparql,
 	return retval;
 }
 
+static gboolean
+check_idempotent_delete (TrackerSparql     *sparql,
+                         TrackerParserNode *pattern,
+                         TrackerParserNode *end)
+{
+	TrackerDBInterface *iface;
+	TrackerParserNode *node, *subject;
+	gint n_triples = 0;
+	gboolean skip = FALSE;
+	gchar *subject_str;
+
+	/* Look for idempotent delete operations (those that don't change
+	 * the RDF graph) or the easy ones at least. If the quad pattern
+	 * consists of a single triple graph, the subject is an IRI, and
+	 * we know it does not exist yet, we can avoid the busywork.
+	 */
+	for (node = tracker_sparql_parser_tree_find_first (pattern, FALSE);
+	     node;
+	     node = tracker_sparql_parser_tree_find_next (node, FALSE)) {
+		const TrackerGrammarRule *rule;
+
+		if (node == end)
+			break;
+
+		rule = tracker_parser_node_get_rule (node);
+		if (tracker_grammar_rule_is_a (rule, RULE_TYPE_RULE,
+		                               NAMED_RULE_TriplesTemplate))
+			n_triples++;
+
+		if (n_triples > 1) {
+			skip = FALSE;
+			break;
+		}
+
+		if (!tracker_grammar_rule_is_a (rule, RULE_TYPE_RULE,
+		                                NAMED_RULE_TriplesSameSubject))
+			continue;
+
+		/* Find subject */
+		subject = tracker_sparql_parser_tree_find_first (node, TRUE);
+
+		/* If it's not an IRI, bail out */
+		rule = tracker_parser_node_get_rule (subject);
+		if (!tracker_grammar_rule_is_a (rule, RULE_TYPE_TERMINAL,
+		                                TERMINAL_TYPE_IRIREF))
+			continue;
+
+		subject_str = _extract_node_string (subject, sparql);
+		iface = tracker_data_manager_get_writable_db_interface (sparql->data_manager);
+		skip = tracker_data_query_resource_id (sparql->data_manager,
+		                                       iface, subject_str) == 0;
+		g_free (subject_str);
+
+		if (!skip)
+			break;
+	}
+
+	return skip;
+}
+
 static gboolean
 translate_DeleteWhere (TrackerSparql  *sparql,
                        GError        **error)
@@ -4515,6 +4575,10 @@ translate_DeleteWhere (TrackerSparql  *sparql,
 
 	quad_pattern = _skip_rule (sparql, NAMED_RULE_QuadPattern);
 
+	if (check_idempotent_delete (sparql, quad_pattern,
+	                             sparql->current_state->node))
+		return TRUE;
+
 	/* 'DELETE WHERE' uses the same pattern for both query and update */
 	solution = get_solution_for_pattern (sparql, quad_pattern, error);
 	if (!solution)
-- 
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