smart_caching.diff

diff --git a/lib/Mojo/Pg.pm b/lib/Mojo/Pg.pm
index 4870d84..8e0769c 100644
--- a/lib/Mojo/Pg.pm
+++ b/lib/Mojo/Pg.pm
@@ -21,8 +21,7 @@ has options => sub {
     AutoCommit          => 1,
     AutoInactiveDestroy => 1,
     PrintError          => 0,
-    RaiseError          => 1,
-    pg_server_prepare   => 0
+    RaiseError          => 1
   };
 };
 has [qw(password username)] => '';
@@ -40,8 +39,13 @@ sub db {
   # Fork-safety
   delete @$self{qw(pid queue)} unless ($self->{pid} //= $$) eq $$;
 
-  my ($dbh, $handle) = @{$self->_dequeue};
-  return Mojo::Pg::Database->new(dbh => $dbh, handle => $handle, pg => $self);
+  my ($dbh, $handle, $sths) = @{$self->_dequeue};
+  return Mojo::Pg::Database->new(
+    dbh    => $dbh,
+    handle => $handle,
+    pg     => $self,
+    queue  => $sths
+  );
 }
 
 sub from_string {
@@ -88,9 +92,9 @@ sub _dequeue {
 }
 
 sub _enqueue {
-  my ($self, $dbh, $handle) = @_;
+  my ($self, $dbh, $handle, $sths) = @_;
   my $queue = $self->{queue} ||= [];
-  push @$queue, [$dbh, $handle] if $dbh->{Active};
+  push @$queue, [$dbh, $handle, $sths] if $dbh->{Active};
   shift @$queue while @$queue > $self->max_connections;
 }
 
diff --git a/lib/Mojo/Pg/Database.pm b/lib/Mojo/Pg/Database.pm
index eb8d0bf..5253841 100644
--- a/lib/Mojo/Pg/Database.pm
+++ b/lib/Mojo/Pg/Database.pm
@@ -11,6 +11,7 @@ use Mojo::Util 'deprecated';
 use Scalar::Util 'weaken';
 
 has [qw(dbh pg)];
+has max_statements => 10;
 
 sub DESTROY {
   my $self = shift;
@@ -19,7 +20,7 @@ sub DESTROY {
   $_->{cb}($self, 'Premature connection close', undef) for @$waiting;
 
   return unless (my $pg = $self->pg) && (my $dbh = $self->dbh);
-  $pg->_enqueue($dbh, $self->{handle});
+  $pg->_enqueue($dbh, @$self{qw(handle queue)});
 }
 
 sub backlog { scalar @{shift->{waiting} || []} }
@@ -35,6 +36,7 @@ sub begin {
 sub disconnect {
   my $self = shift;
   $self->_unwatch;
+  delete $self->{queue};
   $self->dbh->disconnect;
 }
 
@@ -88,19 +90,19 @@ sub query {
   my @values = map { _json($_) ? encode_json $_->{json} : $_ } @_;
 
   # Dollar only
-  my $dbh = $self->dbh;
-  local $dbh->{pg_placeholder_dollaronly} = 1 if delete $self->{dollar_only};
+  local $self->dbh->{pg_placeholder_dollaronly} = 1
+    if delete $self->{dollar_only};
 
   # Blocking
   unless ($cb) {
-    my $sth = $dbh->prepare($query);
+    my $sth = $self->_dequeue($query);
     $sth->execute(@values);
     $self->_notifications;
-    return Mojo::Pg::Results->new(sth => $sth);
+    return Mojo::Pg::Results->new(db => $self, sth => $sth);
   }
 
   # Non-blocking
-  my $sth = $dbh->prepare($query, {pg_async => PG_ASYNC});
+  my $sth = $self->_dequeue($query, 1);
   push @{$self->{waiting}}, {args => \@values, cb => $cb, sth => $sth};
   $self->$_ for qw(_next _watch);
 }
@@ -117,6 +119,25 @@ sub unlisten {
   return $self;
 }
 
+sub _dequeue {
+  my ($self, $query, $async) = @_;
+
+  my $queue = $self->{queue} ||= [];
+  for (my $i = 0; $i <= $#$queue; $i++) {
+    my $sth = $queue->[$i];
+    return splice @$queue, $i, 1
+      if !(!$sth->{pg_async} ^ !$async) && $sth->{Statement} eq $query;
+  }
+
+  return $self->dbh->prepare($query, $async ? {pg_async => PG_ASYNC} : ());
+}
+
+sub _enqueue {
+  my ($self, $sth) = @_;
+  push @{$self->{queue}}, $sth;
+  shift @{$self->{queue}} while @{$self->{queue}} > $self->max_statements;
+}
+
 sub _json { ref $_[0] eq 'HASH' && (keys %{$_[0]})[0] eq 'json' }
 
 sub _next {
@@ -157,7 +178,7 @@ sub _watch {
       my $result = do { local $dbh->{RaiseError} = 0; $dbh->pg_result };
       my $err = defined $result ? undef : $dbh->errstr;
 
-      $self->$cb($err, Mojo::Pg::Results->new(sth => $sth));
+      $self->$cb($err, Mojo::Pg::Results->new(db => $self, sth => $sth));
       $self->_next;
       $self->_unwatch unless $self->backlog || $self->is_listening;
     }
diff --git a/lib/Mojo/Pg/Results.pm b/lib/Mojo/Pg/Results.pm
index 72bf8ca..d802921 100644
--- a/lib/Mojo/Pg/Results.pm
+++ b/lib/Mojo/Pg/Results.pm
@@ -5,7 +5,12 @@ use Mojo::Collection;
 use Mojo::JSON 'decode_json';
 use Mojo::Util 'tablify';
 
-has 'sth';
+has [qw(db sth)];
+
+sub DESTROY {
+  my $self = shift;
+  if ((my $db = $self->db) && (my $sth = $self->sth)) { $db->_enqueue($sth) }
+}
 
 sub array { ($_[0]->_expand($_[0]->sth->fetchrow_arrayref))[0] }
 
diff --git a/t/connection.t b/t/connection.t
index 9400ed8..8526c4b 100644
--- a/t/connection.t
+++ b/t/connection.t
@@ -12,8 +12,7 @@ my $options = {
   AutoCommit          => 1,
   AutoInactiveDestroy => 1,
   PrintError          => 0,
-  RaiseError          => 1,
-  pg_server_prepare   => 0
+  RaiseError          => 1
 };
 is_deeply $pg->options, $options, 'right options';
 
@@ -26,8 +25,7 @@ $options = {
   AutoCommit          => 1,
   AutoInactiveDestroy => 1,
   PrintError          => 0,
-  RaiseError          => 1,
-  pg_server_prepare   => 0
+  RaiseError          => 1
 };
 is_deeply $pg->options, $options, 'right options';
 
@@ -40,8 +38,7 @@ $options = {
   AutoCommit          => 1,
   AutoInactiveDestroy => 1,
   PrintError          => 1,
-  RaiseError          => 1,
-  pg_server_prepare   => 0
+  RaiseError          => 1
 };
 is_deeply $pg->options, $options, 'right options';
 
@@ -55,8 +52,7 @@ $options = {
   AutoCommit          => 1,
   AutoInactiveDestroy => 1,
   PrintError          => 0,
-  RaiseError          => 1,
-  pg_server_prepare   => 0
+  RaiseError          => 1
 };
 is_deeply $pg->options, $options, 'right options';
 
@@ -69,8 +65,7 @@ $options = {
   AutoCommit          => 1,
   AutoInactiveDestroy => 1,
   PrintError          => 0,
-  RaiseError          => 1,
-  pg_server_prepare   => 0
+  RaiseError          => 1
 };
 is_deeply $pg->options, $options, 'right options';
 
@@ -84,8 +79,7 @@ $options = {
   AutoCommit          => 1,
   AutoInactiveDestroy => 1,
   PrintError          => 1,
-  RaiseError          => 0,
-  pg_server_prepare   => 0
+  RaiseError          => 0
 };
 is_deeply $pg->options, $options, 'right options';
 
@@ -98,8 +92,7 @@ $options = {
   AutoCommit          => 1,
   AutoInactiveDestroy => 1,
   PrintError          => 0,
-  RaiseError          => 0,
-  pg_server_prepare   => 0
+  RaiseError          => 0
 };
 is_deeply $pg->options, $options, 'right options';
 
diff --git a/t/database.t b/t/database.t
index 16f42b7..6ef5e02 100644
--- a/t/database.t
+++ b/t/database.t
@@ -73,13 +73,27 @@ is $pg->db->dbh, $dbh, 'same database handle';
 $pg->db->disconnect;
 isnt $pg->db->dbh, $dbh, 'different database handles';
 
+# Statement cache
+$db = $pg->db;
+is $db->max_statements, 10, 'right default';
+my $sth = $db->query('select 3 as three')->sth;
+is $db->query('select 3 as three')->sth,  $sth, 'same statement handle';
+isnt $db->query('select 4 as four')->sth, $sth, 'different statement handles';
+is $db->query('select 3 as three')->sth,  $sth, 'same statement handle';
+undef $db;
+$db = $pg->db->max_statements(2);
+is $db->query('select 3 as three')->sth,   $sth, 'same statement handle';
+isnt $db->query('select 5 as five')->sth,  $sth, 'different statement handles';
+isnt $db->query('select 6 as six')->sth,   $sth, 'different statement handles';
+isnt $db->query('select 3 as three')->sth, $sth, 'different statement handles';
+
 # Dollar only
 $db = $pg->db;
-is $db->dollar_only->query('select $1 as test', 23)->hash->{test}, 23,
+is $db->dollar_only->query('select $1::int as test', 23)->hash->{test}, 23,
   'right result';
-eval { $db->dollar_only->query('select ? as test', 23) };
+eval { $db->dollar_only->query('select ?::int as test', 23) };
 like $@, qr/called with 1 bind variables when 0 are needed/, 'right error';
-is $db->query('select ? as test', 23)->hash->{test}, 23, 'right result';
+is $db->query('select ?::int as test', 23)->hash->{test}, 23, 'right result';
 
 # JSON
 $db = $pg->db;