cindex: speed up initial scan setup phase

This brings a no-op -cindex scan of a git.kernel.org mirror
down from 70s to 10s with a hot cache on a busy machine.

CPU-intensive SHA-256 fingerprinting of the `git show-ref'
result can be parallelized on shard workers.  Future changes can
move more of the initial scan setup phase into shard workers for
more parallelism.

But most of the performance for skipping unchanged repos is
gained from delaying the commit time reading until we've seen
the fingerprint is out-of-date, since reading commit times
requires a large amount of I/O compared to only reading refs
for fingerprints.

1 files changed, 53 insertions, 46 deletions

diff --git a/lib/PublicInbox/CodeSearchIdx.pm b/lib/PublicInbox/CodeSearchIdx.pm
index 555a1efe..ec0fc6e3 100644
--- a/lib/PublicInbox/CodeSearchIdx.pm
+++ b/lib/PublicInbox/CodeSearchIdx.pm
@@ -105,6 +105,7 @@ our (
         @JOIN_DT, # YYYYmmddHHMMSS for dt:
         $QRY_STR, # common query string for both code and inbox associations
         $DUMP_IBX_WPIPE, # goes to sort(1)
+        $ANY_SHARD, # shard round-robin for scan fingerprinting
         @OFF2ROOT,
 );
 
@@ -416,51 +417,42 @@ sub run_git {
 
 # this is different from the grokmirror-compatible fingerprint since we
 # only care about --heads (branches) and --tags, and not even their names
-sub fp_start ($$$) {
-        my ($self, $git, $prep_repo) = @_;
+sub fp_start ($$) {
+        my ($self, $git) = @_;
         return if $DO_QUIT;
         open my $refs, '+>', undef;
         $git->{-repo}->{refs} = $refs;
-        run_git([qw(show-ref --heads --tags --hash)], { 1 => $refs },
-                \&fp_fini, $self, $git, $prep_repo);
-}
-
-sub fp_fini { # run_git cb
-        my (undef, $self, $git, $prep_repo) = @_;
-        my $refs = $git->{-repo}->{refs} // die 'BUG: no {-repo}->{refs}';
-        sysseek($refs, 0, SEEK_SET);
-        $git->{-repo}->{fp} = sha_all(256, $refs)->hexdigest;
+        my ($c, $p) = PublicInbox::PktOp->pair;
+        my $next_on_err = PublicInbox::OnDestroy->new(\&index_next, $self);
+        $c->{ops}->{fp_done} = [ $self, $git, $next_on_err ];
+        $IDX_SHARDS[++$ANY_SHARD % scalar(@IDX_SHARDS)]->wq_io_do('fp_async',
+                                        [ $p->{op_p}, $refs ], $git->{git_dir})
 }
 
-sub ct_start ($$$) {
-        my ($self, $git, $prep_repo) = @_;
-        return if $DO_QUIT;
-        run_git([ qw[for-each-ref --sort=-committerdate
-                --format=%(committerdate:raw) --count=1
-                refs/heads/ refs/tags/] ], undef, # capture like qx
-                \&ct_fini, $self, $git, $prep_repo);
+sub fp_async { # via wq_io_do in worker
+        my ($self, $git_dir) = @_;
+        my $op_p = delete $self->{0} // die 'BUG: no {0} op_p';
+        my $refs = delete $self->{1} // die 'BUG: no {1} refs';
+        my $git = PublicInbox::Git->new($git_dir);
+        run_git([qw(show-ref --heads --tags --hash)], { 1 => $refs },
+                \&fp_async_done, $self, $git, $op_p);
 }
 
-sub ct_fini { # run_git cb
-        my ($opt, $self, $git, $prep_repo) = @_;
-        my ($ct) = split(/\s+/, ${$opt->{1}}); # drop TZ + LF
-        $git->{-repo}->{ct} = $ct + 0;
+sub fp_async_done { # run_git cb from worker
+        my ($opt, $self, $git, $op_p) = @_;
+        my $refs = delete $opt->{1} // 'BUG: no {-repo}->{refs}';
+        sysseek($refs, 0, SEEK_SET);
+        send($op_p, 'fp_done '.sha_all(256, $refs)->hexdigest, 0);
 }
 
-# TODO: also index gitweb.owner and the full fingerprint for grokmirror?
-sub prep_repo ($$) {
-        my ($self, $git) = @_;
+sub fp_done { # called parent via PktOp by fp_async_done
+        my ($self, $git, $next_on_err, $hex) = @_;
+        $next_on_err->cancel;
         return if $DO_QUIT;
-        return index_next($self) if $git->{-cidx_err};
-        my $repo = $git->{-repo} // die 'BUG: no {-repo}';
-        if (!defined($repo->{ct})) {
-                warn "W: $git->{git_dir} has no commits, skipping\n";
-                delete $git->{-repo};
-                return index_next($self);
-        }
+        $git->{-repo}->{fp} = $hex;
         my $n = git_dir_hash($git->{git_dir}) % scalar(@RDONLY_XDB);
         my $shard = bless { %$self, shard => $n }, ref($self);
-        $repo->{shard_n} = $n;
+        $git->{-repo}->{shard_n} = $n;
         delete @$shard{qw(lockfh lock_path)};
         local $shard->{xdb} = $RDONLY_XDB[$n] // die "BUG: shard[$n] undef";
         $shard->retry_reopen(\&check_existing, $self, $git);
@@ -469,7 +461,7 @@ sub prep_repo ($$) {
 sub check_existing { # retry_reopen callback
         my ($shard, $self, $git) = @_;
         my @docids = $shard->docids_of_git_dir($git->{git_dir});
-        my $docid = shift(@docids) // return get_roots($self, $git);
+        my $docid = shift(@docids) // return prep_repo($self, $git); # new repo
         my $doc = $shard->get_doc($docid) //
                         die "BUG: no #$docid ($git->{git_dir})";
         my $old_fp = $REINDEX ? "\0invalid" : $doc->get_data;
@@ -482,7 +474,7 @@ sub check_existing { # retry_reopen callback
                 warn "BUG: $git->{git_dir} indexed multiple times, culling\n";
                 $git->{-repo}->{to_delete} = \@docids; # XXX needed?
         }
-        get_roots($self, $git);
+        prep_repo($self, $git);
 }
 
 sub partition_refs ($$$) {
@@ -604,13 +596,9 @@ sub index_next ($) {
         my ($self) = @_;
         return if $DO_QUIT;
         if ($IDXQ && @$IDXQ) {
-                index_repo(undef, $self, shift @$IDXQ);
+                index_repo($self, shift @$IDXQ);
         } elsif ($SCANQ && @$SCANQ) {
-                my $git = shift @$SCANQ;
-                my $prep_repo = PublicInbox::OnDestroy->new(\&prep_repo,
-                                                                $self, $git);
-                fp_start($self, $git, $prep_repo);
-                ct_start($self, $git, $prep_repo);
+                fp_start $self, shift @$SCANQ;
         } elsif ($TMPDIR) {
                 delete $TODO{dump_roots_start};
                 delete $TODO{dump_ibx_start}; # runs OnDestroy once
@@ -649,12 +637,17 @@ sub index_done { # OnDestroy cb called when done indexing each code repo
         # repo_stored will fire once store_repo is done
 }
 
-sub index_repo { # run_git cb
-        my (undef, $self, $git) = @_;
+sub index_repo {
+        my ($self, $git) = @_;
         return if $DO_QUIT;
+        my $repo = $git->{-repo} // die 'BUG: no {-repo}';
         return index_next($self) if $git->{-cidx_err};
+        if (!defined($repo->{ct})) {
+                warn "W: $git->{git_dir} has no commits, skipping\n";
+                return index_next($self);
+        }
         return push(@$IDXQ, $git) if $REPO_CTX; # busy
-        my $repo = delete $git->{-repo} or return index_next($self);
+        delete $git->{-repo};
         my $roots_fh = delete $repo->{roots_fh} // die 'BUG: no {roots_fh}';
         seek($roots_fh, 0, SEEK_SET);
         chomp(my @roots = PublicInbox::IO::read_all $roots_fh);
@@ -685,15 +678,28 @@ sub index_repo { # run_git cb
         # shard_done fires when shard_index is done
 }
 
-sub get_roots ($$) {
+sub ct_fini { # run_git cb
+        my ($opt, $self, $git, $index_repo) = @_;
+        my ($ct) = split(/\s+/, ${$opt->{1}}); # drop TZ + LF
+        $git->{-repo}->{ct} = $ct + 0;
+}
+
+# TODO: also index gitweb.owner and the full fingerprint for grokmirror?
+sub prep_repo ($$) {
         my ($self, $git) = @_;
         return if $DO_QUIT;
+        my $index_repo = PublicInbox::OnDestroy->new(\&index_repo, $self, $git);
         my $refs = $git->{-repo}->{refs} // die 'BUG: no {-repo}->{refs}';
         sysseek($refs, 0, SEEK_SET);
         open my $roots_fh, '+>', undef;
         $git->{-repo}->{roots_fh} = $roots_fh;
         run_git([ qw(rev-list --stdin --max-parents=0) ],
-                { 0 => $refs, 1 => $roots_fh }, \&index_repo, $self, $git)
+                { 0 => $refs, 1 => $roots_fh }, \&PublicInbox::Config::noop,
+                $self, $git, $index_repo);
+        run_git([ qw[for-each-ref --sort=-committerdate
+                --format=%(committerdate:raw) --count=1
+                refs/heads/ refs/tags/] ], undef, # capture like qx
+                \&ct_fini, $self, $git, $index_repo);
 }
 
 # for PublicInbox::SearchIdx `git patch-id' call and with_umask
@@ -1295,6 +1301,7 @@ sub cidx_run { # main entry point
                 init_join_prefork($self)
         }
         local @IDX_SHARDS = cidx_init($self); # forks workers
+        local $ANY_SHARD = -1;
         local $self->{current_info} = '';
         local $MY_SIG = {
                 CHLD => \&PublicInbox::DS::enqueue_reap,