add test for issue_260

Only for posterity... See notes in the test file for how to use it. Test is
normally skipped. Will cause an assert under old versions of memcached.

t/issue_260.t

@@ -0,0 +1,83 @@
+#!/usr/bin/perl
+# Issue #260 is a terrible bug.
+# In order to run this test:
+# * checkout 1.4.15
+# * change TAIL_REPAIR_TIME from (3 * 3600) to 3
+# Now it should cause an assert. Patches can be tested to fix it.
+
+use strict;
+use Test::More;
+use FindBin qw($Bin);
+use lib "$Bin/lib";
+use MemcachedTest;
+
+plan skip_all => "Only possible to test #260 under artificial conditions";
+exit 0;
+plan tests => 11074;
+# assuming max slab is 1M and default mem is 64M
+my $server = new_memcached();
+my $sock = $server->sock;
+
+# create a big value for the largest slab
+my $max = 1024 * 1024;
+my $big = 'x' x (1024 * 1024 - 250);
+
+ok(length($big) > 512 * 1024);
+ok(length($big) < 1024 * 1024);
+
+# set the big value
+my $len = length($big);
+print $sock "set big 0 0 $len\r\n$big\r\n";
+is(scalar <$sock>, "STORED\r\n", "stored big");
+mem_get_is($sock, "big", $big);
+
+# no evictions yet
+my $stats = mem_stats($sock);
+is($stats->{"evictions"}, "0", "no evictions to start");
+
+# set many big items, enough to get evictions
+for (my $i = 0; $i < 100; $i++) {
+  print $sock "set item_$i 0 0 $len\r\n$big\r\n";
+  is(scalar <$sock>, "STORED\r\n", "stored item_$i");
+}
+
+# some evictions should have happened
+my $stats = mem_stats($sock);
+my $evictions = int($stats->{"evictions"});
+ok($evictions == 37, "some evictions happened");
+
+# the first big value should be gone
+mem_get_is($sock, "big", undef);
+
+# the earliest items should be gone too
+for (my $i = 0; $i < $evictions - 1; $i++) {
+  mem_get_is($sock, "item_$i", undef);
+}
+
+# check that the non-evicted are the right ones
+for (my $i = $evictions - 1; $i < $evictions + 4; $i++) {
+  mem_get_is($sock, "item_$i", $big);
+}
+
+# Now we fill a slab with incrementable items...
+for (my $i = 0; $i < 10923; $i++) {
+  print $sock "set sitem_$i 0 0 1\r\n1\r\n";
+  is(scalar <$sock>, "STORED\r\n", "stored sitem_$i");
+}
+
+my $stats = mem_stats($sock);
+my $evictions = int($stats->{"evictions"});
+ok($evictions == 38, "one more eviction happened: $evictions");
+
+# That evicted item was the first one we put in.
+mem_get_is($sock, "sitem_0", undef);
+
+sleep 15;
+
+# Now we increment the item which should be on the tail.
+# THIS asserts the memcached-debug binary.
+print $sock "incr sitem_1 1\r\n";
+is(scalar <$sock>, "2\r\n", "incremented to two");
+
+#my $stats = mem_stats($sock, "slabs");
+#is($stats->{"1:free_chunks"}, 0, "free chunks should still be 0");