Added recall test

test/t/003_recall.pl

@@ -0,0 +1,41 @@
+use strict;
+use warnings;
+use PostgresNode;
+use TestLib;
+use Test::More tests => 1;
+
+# Initialize node
+my $node = get_new_node('node');
+$node->init;
+$node->start;
+
+# Create table
+$node->safe_psql("postgres", "CREATE EXTENSION vector;");
+$node->safe_psql("postgres", "CREATE TABLE tst (i int4, v vector(3));");
+$node->safe_psql("postgres",
+  "INSERT INTO tst SELECT i, ARRAY[random(), random(), random()] FROM generate_series(1,100000) i;"
+);
+
+# Get exact results
+my $expected = $node->safe_psql("postgres", "SELECT i FROM tst ORDER BY v <-> '[0.5,0.5,0.5]' LIMIT 10;");
+my @expected_ids = split("\n", $expected);
+
+# Add index
+$node->safe_psql("postgres", "CREATE INDEX ON tst USING ivfflat (v);");
+
+# Get approximate results
+$node->safe_psql("postgres", "SET enable_seqscan = off;");
+my $actual = $node->safe_psql("postgres", "SELECT i FROM tst ORDER BY v <-> '[0.5,0.5,0.5]' LIMIT 10;");
+my @actual_ids = split("\n", $actual);
+my %actual_set = map { $_ => 1 } @actual_ids;
+
+my $count = 0;
+for my $el (@expected_ids) {
+  if (exists($actual_set{$el})) {
+    $count++;
+  }
+}
+
+# TODO Run more queries to prevent flakiness
+# TODO Test ivfflat.probes
+cmp_ok($count, ">=", 5);