From 90dd96e08fcac4c1d4e8761a108553d3e039f52a Mon Sep 17 00:00:00 2001
From: Daniel Friesel <derf@finalrewind.org>
Date: Sat, 20 Jul 2019 20:58:28 +0200
Subject: Handle race condition when several workers are updating the same
history entry
---
lib/Travelynx.pm | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/lib/Travelynx.pm b/lib/Travelynx.pm
index 3ef7011..2bc151d 100755
--- a/lib/Travelynx.pm
+++ b/lib/Travelynx.pm
@@ -1485,15 +1485,33 @@ sub startup {
);
my $stats = $self->compute_journey_stats(@journeys);
- $self->pg->db->insert(
- 'journey_stats',
+ eval {
+ $self->pg->db->insert(
+ 'journey_stats',
+ {
+ user_id => $uid,
+ year => $year,
+ month => $month,
+ data => JSON->new->encode($stats),
+ }
+ );
+ };
+ if ( my $err = $@ ) {
+ if ( $err =~ m{duplicate key value violates unique constraint} )
{
- user_id => $uid,
- year => $year,
- month => $month,
- data => JSON->new->encode($stats),
+ # When a user opens the same history page several times in
+ # short succession, there is a race condition where several
+ # Mojolicious workers execute this helper, notice that there is
+ # no up-to-date history, compute it, and insert it using the
+ # statement above. This will lead to a uniqueness violation
+ # in each successive insert. However, this is harmless, and
+ # thus ignored.
}
- );
+ else {
+ # Otherwise we probably have a problem.
+ die($@);
+ }
+ }
return $stats;
}
--
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