extstore: add ext_drop_unread option + live tune

was struggling to figure out how to automatically turn this on or off, but I
think it should be part of an outside process.

ie; a mechanism should be able to target a specific write rate, and one of
its tools for reducing the write rate should be flipping this on.

there's *still* a hole where you can't trigger a compaction attempt if
there's no fragmentation. I kind of want, if this feature is on, to attempt
a compaction on the oldest page while dropping unread items.

1 files changed, 9 insertions, 0 deletions

diff --git a/t/extstore.t b/t/extstore.t
index 8a8180e..4963ca6 100644
--- a/t/extstore.t
+++ b/t/extstore.t
@@ -100,6 +100,13 @@ mem_get_is($sock, "foo", "hi");
     is($stats->{extstore_pages_free}, 0, '0 pages are free');
     is($stats->{miss_from_extstore}, 1, 'exactly one miss');
 
+    # refresh some keys so rescues happen while drop_unread == 1.
+    for (1 .. $keycount / 2) {
+        next unless $_ % 2 == 1;
+        print $sock "touch mfoo$_ 0 noreply\r\n";
+    }
+    print $sock "extstore drop_unread 1\r\n";
+    my $res = <$sock>;
     for (1 .. $keycount) {
         next unless $_ % 2 == 0;
         print $sock "delete mfoo$_ noreply\r\n";
@@ -110,6 +117,8 @@ mem_get_is($sock, "foo", "hi");
     cmp_ok($stats->{extstore_pages_free}, '>', 0, 'some pages now free');
     cmp_ok($stats->{extstore_compact_rescues}, '>', 0, 'some compaction rescues happened');
     cmp_ok($stats->{extstore_compact_skipped}, '>', 0, 'some compaction skips happened');
+    print $sock "extstore drop_unread 0\r\n";
+    $res = <$sock>;
 }
 
 # attempt to incr/decr/append/prepend or chunk objects that were sent to disk.