From 4d94e4169a9aeb1f2ccde25b2c7debffe6f82cbe Mon Sep 17 00:00:00 2001
From: "mkanat%bugzilla.org" <>
Date: Mon, 3 Aug 2009 14:44:00 +0000
Subject: Bug 508023: Speed up MySQL's bz_alter_column for when we're just
 adding or removing a DEFAULT Patch by Max Kanat-Alexander
 <mkanat@bugzilla.org> (module owner) a=mkanat

---
 Bugzilla/DB/Schema/Mysql.pm | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

(limited to 'Bugzilla/DB')

diff --git a/Bugzilla/DB/Schema/Mysql.pm b/Bugzilla/DB/Schema/Mysql.pm
index 627716970..49e6add1a 100644
--- a/Bugzilla/DB/Schema/Mysql.pm
+++ b/Bugzilla/DB/Schema/Mysql.pm
@@ -178,13 +178,33 @@ sub get_alter_column_ddl {
         delete $new_def_copy{PRIMARYKEY};
     }
 
-    my $new_ddl = $self->get_type_ddl(\%new_def_copy);
     my @statements;
 
     push(@statements, "UPDATE $table SET $column = $set_nulls_to
                         WHERE $column IS NULL") if defined $set_nulls_to;
-    push(@statements, "ALTER TABLE $table CHANGE COLUMN 
+
+    # Calling SET DEFAULT or DROP DEFAULT is *way* faster than calling
+    # CHANGE COLUMN, so just do that if we're just changing the default.
+    my %old_defaultless = %$old_def;
+    my %new_defaultless = %$new_def;
+    delete $old_defaultless{DEFAULT};
+    delete $new_defaultless{DEFAULT};
+    if ($self->columns_equal(\%new_defaultless, \%old_defaultless)) {
+        if (defined $old_def->{DEFAULT} and !defined $new_def->{DEFAULT}) {
+            push(@statements,
+                 "ALTER TABLE $table ALTER COLUMN $column DROP DEFAULT");
+        }
+        else {
+            push(@statements, "ALTER TABLE $table ALTER COLUMN $column 
+                               SET DEFAULT " . $new_def->{DEFAULT});
+        }
+    }
+    else {
+        my $new_ddl = $self->get_type_ddl(\%new_def_copy);
+        push(@statements, "ALTER TABLE $table CHANGE COLUMN 
                        $column $column $new_ddl");
+    }
+
     if ($old_def->{PRIMARYKEY} && !$new_def->{PRIMARYKEY}) {
         # Dropping a PRIMARY KEY needs an explicit DROP PRIMARY KEY
         push(@statements, "ALTER TABLE $table DROP PRIMARY KEY");
-- 
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