extindex: support --dedupe[=MSGID]

Sometimes I just want to dedupe a single Message-ID to test
something, and this lets me do it.

This patch appears to do what its supposed to.  But it also
appears to be finding duplicates that were previously missed.
That's a good thing, but I wish I understood what seems to be
fixed :x

I'm not sure why the previous ExtSearchIdx.pm (blob 357312b8)
was causing messages to be missed, even, and why this patch
seems to fix it...  And it's not infinite looping, either.

Anyways, before this patch, "-extindex --dedupe" was taking ~5
min to no-op every message (after the initial full --dedupe run
which took over a day to run).  No-op --dedupes now take just
under 2 hours to scan every single cross-posted message for a
no-op dedupe.  The initial dedupe took nearly 44 hours on my
system for <https://yhbt.net/lore/all/> due to SATA-2 TLC SSD
latency on 3 gigantic Xapian shards.

Running --dedupe with this change seems to prevent
/BUG\?.*?not deduplicated properly/ stderr messages from being
triggered by View.pm.  Current versions of -extindex do not
seem susceptible to introducing duplicates.

2 files changed, 20 insertions, 9 deletions

diff --git a/lib/PublicInbox/ExtSearchIdx.pm b/lib/PublicInbox/ExtSearchIdx.pm
index 357312b8..2311161e 100644
--- a/lib/PublicInbox/ExtSearchIdx.pm
+++ b/lib/PublicInbox/ExtSearchIdx.pm
@@ -887,23 +887,32 @@ sub dd_smsg { # git->cat_async callback
         }
 }
 
-sub eidx_dedupe ($$) {
-        my ($self, $sync) = @_;
+sub eidx_dedupe ($$$) {
+        my ($self, $sync, $msgids) = @_;
         $sync->{dedupe_cull} = 0;
         my $candidates = 0;
         my $nr_mid = 0;
         return unless eidxq_lock_acquire($self);
-        my $iter;
+        my ($iter, $cur_mid);
         my $min_id = 0;
+        my $idx = 0;
         local $sync->{-regen_fmt} = "dedupe %u/".$self->{oidx}->max."\n";
 
         # note: we could write this query more intelligently,
         # but that causes lock contention with read-only processes
 dedupe_restart:
-        $iter = $self->{oidx}->dbh->prepare(<<EOS);
+        $cur_mid = $msgids->[$idx];
+        if ($cur_mid eq '') { # all Message-IDs
+                $iter = $self->{oidx}->dbh->prepare(<<EOS);
 SELECT mid,id FROM msgid WHERE id > ? ORDER BY id ASC
 EOS
-        $iter->execute($min_id);
+                $iter->execute($min_id);
+        } else {
+                $iter = $self->{oidx}->dbh->prepare(<<EOS);
+SELECT mid,id FROM msgid WHERE mid = ? AND id > ? ORDER BY id ASC
+EOS
+                $iter->execute($cur_mid, $min_id);
+        }
         while (my ($mid, $id) = $iter->fetchrow_array) {
                 last if $sync->{quit};
                 $self->{current_info} = "dedupe $mid";
@@ -937,6 +946,8 @@ EOS
                         goto dedupe_restart;
                 }
         }
+        goto dedupe_restart if defined($msgids->[++$idx]);
+
         my $n = delete $sync->{dedupe_cull};
         if (my $pr = $sync->{-opt}->{-progress}) {
                 $pr->("culled $n/$candidates candidates ($nr_mid msgids)\n");
@@ -974,9 +985,9 @@ sub eidx_sync { # main entry point
         for my $ibx (@{ibx_sorted($self)}) {
                 $ibx->{-ibx_id} //= $self->{oidx}->ibx_id($ibx->eidx_key);
         }
-        if (delete($opt->{dedupe})) {
+        if (my $msgids = delete($opt->{dedupe})) {
                 local $sync->{checkpoint_unlocks} = 1;
-                eidx_dedupe($self, $sync);
+                eidx_dedupe($self, $sync, $msgids);
         }
         if (delete($opt->{reindex})) {
                 local $sync->{checkpoint_unlocks} = 1;
diff --git a/script/public-inbox-extindex b/script/public-inbox-extindex
index dcb12e5a..addd5ac6 100755
--- a/script/public-inbox-extindex
+++ b/script/public-inbox-extindex
@@ -17,7 +17,7 @@ usage: public-inbox-extindex [options] [EXTINDEX_DIR] [INBOX_DIR...]
   --batch-size=BYTES  flush changes to OS after a given number of bytes
   --max-size=BYTES    do not index messages larger than the given size
   --gc                perform garbage collection instead of indexing
-  --dedupe            fix prior deduplication errors
+  --dedupe[=MSGID]    fix prior deduplication errors (may be repeated)
   --verbose | -v      increase verbosity (may be repeated)
   --dry-run | -n      dry-run on --dedupe
 
@@ -29,7 +29,7 @@ GetOptions($opt, qw(verbose|v+ reindex rethread compact|c+ jobs|j=i
                 fsync|sync!
                 indexlevel|index-level|L=s max_size|max-size=s
                 batch_size|batch-size=s
-                dedupe gc commit-interval=i watch scan! dry-run|n
+                dedupe:s@ gc commit-interval=i watch scan! dry-run|n
                 all help|h))
         or die $help;
 if ($opt->{help}) { print $help; exit 0 };