[WIP] extindex: support --dedupe[=MSGID]

[Eric Wong <e@80x24.org>]

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 I seem to have
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).  Now that it appears to be doing
many more dedupes, so it could take 40-ish hours to finish the
dedupe run on the machine running <https://yhbt.net/lore/all/>.

Hopefully this will result in "BUG?" messages from View.pm going
away after it finishes.

-------8<------
Subject: [PATCH] extindex: support --dedupe[=MSGID]

Sometimes I just want to dedupe a single Message-ID to test
something, and this lets me do it.
---
 lib/PublicInbox/ExtSearchIdx.pm | 24 +++++++++++++++++-------
 script/public-inbox-extindex    |  4 ++--
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/lib/PublicInbox/ExtSearchIdx.pm b/lib/PublicInbox/ExtSearchIdx.pm
index 357312b8..442ded46 100644
--- a/lib/PublicInbox/ExtSearchIdx.pm
+++ b/lib/PublicInbox/ExtSearchIdx.pm
@@ -887,23 +887,31 @@ 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;
 	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);
+	$cur_mid = shift @$msgids;
+	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 $mid";
@@ -937,6 +945,8 @@ EOS
 			goto dedupe_restart;
 		}
 	}
+	goto dedupe_restart if scalar(@$msgids);
+
 	my $n = delete $sync->{dedupe_cull};
 	if (my $pr = $sync->{-opt}->{-progress}) {
 		$pr->("culled $n/$candidates candidates ($nr_mid msgids)\n");
@@ -974,9 +984,9 @@ 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 };