From patchwork Fri Oct 28 14:42:27 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Patrick Steinhardt X-Patchwork-Id: 13023790 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44693ECAAA1 for ; Fri, 28 Oct 2022 14:43:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229846AbiJ1Om6 (ORCPT ); Fri, 28 Oct 2022 10:42:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52402 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229972AbiJ1Omd (ORCPT ); Fri, 28 Oct 2022 10:42:33 -0400 Received: from out5-smtp.messagingengine.com (out5-smtp.messagingengine.com [66.111.4.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 399991D3E94 for ; Fri, 28 Oct 2022 07:42:30 -0700 (PDT) Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailout.nyi.internal (Postfix) with ESMTP id A398C5C00C2 for ; Fri, 28 Oct 2022 10:42:29 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute4.internal (MEProxy); Fri, 28 Oct 2022 10:42:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pks.im; h=cc :content-type:date:date:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:sender:subject :subject:to:to; s=fm3; t=1666968149; x=1667054549; bh=Kz9wSJMi82 Vwhy8R25UVQPkyLqMgrLWhJJAybFTLSr0=; b=TX0ywOYWjOH+DMlzVpuN47KPdb EdGCZ9qJ4JGbecm8p40klqKH2ix2B6j0cZJX6MTL2/4NpnqRdhqzrCbPyLeDBgID jP/uAl1ExcCp8eNw8K4Dkbqcx5/3o3Sk0J7Oce2pXhl1ot7Fz1f0q3KC7aIR3oMX CHqlkRv+VEPEoIpo4U1XDEZ4CAc20ROftrD/1iWspQYgEUqU7ZBK5VHOUewBVbbP EYvBXrvgbb9UHxqW9VvUyuqxVQ8q1HGAfu7AgGxyNrhiMzYaX637Q0g7+7DtBCGa 6wU1HycgRwiYJ+QZqiYNXJwDVeTzWEcHO03DLgOZzSiPJ5lkKWzKKwV+2guA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-type:date:date:feedback-id :feedback-id:from:from:in-reply-to:in-reply-to:message-id :mime-version:references:reply-to:sender:subject:subject:to:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm3; t=1666968149; x=1667054549; bh=Kz9wSJMi82Vwhy8R25UVQPkyLqMg rLWhJJAybFTLSr0=; b=Xe8sAn0IuvUek/CM8hH0FUMdfAxtEAnb4C0ikm8lLhER ZU6w9o0Oqidwp8S6qbGQ3/wKZawk7EsFJuFpGE9zcyJc8LlMRKqNHUEMrEPwdi+N Q0N33sOiFEk/hqmbdTC1Filc0UJZBUEOP3PqyB5PihdKOdfmCZ4GreDDonD7+/vz /VGm+QSZuBrzUansKRrQanHCtseP/vzTbFB+b9qhnjX3SaLCQbZ8Q1/4zGcP6KEh jUeTInRVaVJXtgS1HZGrQ5NdEKb+fP6SjA46Z7UfOMCMOMlQLbASmDXTvQhPIt8U qSJb04+noCImsZ+B2tm0KCQj6+M0QT1lUjmuqslTKw== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvgedrtdeigdejkecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecunecujfgurhepfffhvffukfhfgggtuggjsehgtderre dttdejnecuhfhrohhmpefrrghtrhhitghkucfuthgvihhnhhgrrhguthcuoehpshesphhk shdrihhmqeenucggtffrrghtthgvrhhnpeehgfejueevjeetudehgffffeffvdejfeejie dvkeffgfekuefgheevteeufeelkeenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgr mhepmhgrihhlfhhrohhmpehpshesphhkshdrihhm X-ME-Proxy: Feedback-ID: i197146af:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA for ; Fri, 28 Oct 2022 10:42:28 -0400 (EDT) Received: by pks.im (OpenSMTPD) with ESMTPSA id ea34f43a (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO) for ; Fri, 28 Oct 2022 14:42:22 +0000 (UTC) Date: Fri, 28 Oct 2022 16:42:27 +0200 From: Patrick Steinhardt To: git@vger.kernel.org Subject: [PATCH 2/2] receive-pack: use advertised reference tips to inform connectivity check Message-ID: <006e89f384be1227b922fb6fdc8755ae84cac587.1666967670.git.ps@pks.im> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org When serving a push, git-receive-pack(1) needs to verify that the packfile sent by the client contains all objects that are required by the updated references. This connectivity check works by marking all preexisting references as uninteresting and using the new reference tips as starting point for a graph walk. This strategy has the major downside that it will not require any object to be sent by the client that is reachable by any of the repositories' references. While that sounds like it would be indeed what we are after with the connectivity check, it is arguably not. The administrator that manages the server-side Git repository may have configured certain refs to be hidden during the reference advertisement via `transfer.hideRefs` or `receivepack.hideRefs`. Whatever the reason, the result is that the client shouldn't expect that any of those hidden references exists on the remote side, and neither should they assume any of the pointed-to objects to exist except if referenced by any visible reference. But because we treat _all_ local refs as uninteresting in the connectivity check, a client is free to send a packfile that references objects that are only reachable via a hidden reference on the server-side, and we will gladly accept it. Besides the correctness issue there is also a performance issue. Git forges tend to do internal bookkeeping to keep alive sets of objects for internal use or make them easy to find via certain references. These references are typically hidden away from the user so that they are neither advertised nor writeable. At GitLab, we have one particular repository that contains a total of 7 million references, of which 6.8 million are indeed internal references. With the current connectivity check we are forced to load all these references in order to mark them as uninteresting, and this alone takes around 15 seconds to compute. We can fix both of these issues by changing the logic for stateful invocations of git-receive-pack(1) where the reference advertisement and packfile negotiation are served by the same process. Instead of marking all preexisting references as unreachable, we will only mark those that we have announced to the client. Besides the stated fix to correctness this also provides a huge boost to performance in the repository mentioned above. Pushing a new commit into this repo with `transfer.hideRefs` set up to hide 6.8 million of 7 refs as it is configured in Gitaly leads to an almost 7.5-fold speedup: Benchmark 1: main Time (mean ± σ): 29.902 s ± 0.105 s [User: 29.176 s, System: 1.052 s] Range (min … max): 29.781 s … 29.969 s 3 runs Benchmark 2: pks-connectivity-check-hide-refs Time (mean ± σ): 4.033 s ± 0.088 s [User: 4.071 s, System: 0.374 s] Range (min … max): 3.953 s … 4.128 s 3 runs Summary 'pks-connectivity-check-hide-refs' ran 7.42 ± 0.16 times faster than 'main' Unfortunately, this change comes with a performance hit when refs are not hidden. Executed in the same repository: Benchmark 1: main Time (mean ± σ): 45.780 s ± 0.507 s [User: 46.908 s, System: 4.838 s] Range (min … max): 45.453 s … 46.364 s 3 runs Benchmark 2: pks-connectivity-check-hide-refs Time (mean ± σ): 49.886 s ± 0.282 s [User: 51.168 s, System: 5.015 s] Range (min … max): 49.589 s … 50.149 s 3 runs Summary 'main' ran 1.09 ± 0.01 times faster than 'pks-connectivity-check-hide-refs' This is probably caused by the overhead of reachable tips being passed in via git-rev-list(1)'s standard input, which seems to be slower than reading the references from disk. It is debatable what to do about this. If this were only about improving performance then it would be trivial to make the new logic depend on whether or not `transfer.hideRefs` has been configured in the repo. But as explained this is also about correctness, even though this can be considered an edge case. Furthermore, this slowdown is really only noticeable in outliers like the above repository with an unreasonable amount of refs. The same benchmark in linux-stable.git with about 4500 references shows no measurable difference: Benchmark 1: main Time (mean ± σ): 375.4 ms ± 25.4 ms [User: 312.2 ms, System: 155.7 ms] Range (min … max): 324.2 ms … 492.9 ms 50 runs Benchmark 2: pks-connectivity-check-hide-refs Time (mean ± σ): 374.9 ms ± 36.9 ms [User: 311.6 ms, System: 158.2 ms] Range (min … max): 319.2 ms … 583.1 ms 50 runs Summary 'pks-connectivity-check-hide-refs' ran 1.00 ± 0.12 times faster than 'main' Let's keep this as-is for the time being and accept the performance hit. It is arguably extremely noticeable to a user if a push now performs 7.5 times faster than before, but a lot less so in case an already-slow push becomes about 10% slower. Signed-off-by: Patrick Steinhardt --- builtin/receive-pack.c | 31 ++++++++++++++++++++++--------- 1 file changed, 22 insertions(+), 9 deletions(-) diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c index 44bcea3a5b..50794539c6 100644 --- a/builtin/receive-pack.c +++ b/builtin/receive-pack.c @@ -326,13 +326,10 @@ static void show_one_alternate_ref(const struct object_id *oid, show_ref(".have", oid); } -static void write_head_info(void) +static void write_head_info(struct oidset *announced_objects) { - static struct oidset seen = OIDSET_INIT; - - for_each_ref(show_ref_cb, &seen); - for_each_alternate_ref(show_one_alternate_ref, &seen); - oidset_clear(&seen); + for_each_ref(show_ref_cb, announced_objects); + for_each_alternate_ref(show_one_alternate_ref, announced_objects); if (!sent_capabilities) show_ref("capabilities^{}", null_oid()); @@ -1896,12 +1893,20 @@ static void execute_commands_atomic(struct command *commands, strbuf_release(&err); } +static const struct object_id *iterate_announced_oids(void *cb_data) +{ + struct oidset_iter *iter = cb_data; + return oidset_iter_next(iter); +} + static void execute_commands(struct command *commands, const char *unpacker_error, struct shallow_info *si, - const struct string_list *push_options) + const struct string_list *push_options, + struct oidset *announced_oids) { struct check_connected_options opt = CHECK_CONNECTED_INIT; + struct oidset_iter announced_oids_iter; struct command *cmd; struct iterate_data data; struct async muxer; @@ -1928,6 +1933,12 @@ static void execute_commands(struct command *commands, opt.err_fd = err_fd; opt.progress = err_fd && !quiet; opt.env = tmp_objdir_env(tmp_objdir); + if (oidset_size(announced_oids) != 0) { + oidset_iter_init(announced_oids, &announced_oids_iter); + opt.reachable_oids_fn = iterate_announced_oids; + opt.reachable_oids_data = &announced_oids_iter; + } + if (check_connected(iterate_receive_command_list, &data, &opt)) set_connectivity_errors(commands, si); @@ -2462,6 +2473,7 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix) { int advertise_refs = 0; struct command *commands; + struct oidset announced_oids = OIDSET_INIT; struct oid_array shallow = OID_ARRAY_INIT; struct oid_array ref = OID_ARRAY_INIT; struct shallow_info si; @@ -2524,7 +2536,7 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix) } if (advertise_refs || !stateless_rpc) { - write_head_info(); + write_head_info(&announced_oids); } if (advertise_refs) return 0; @@ -2554,7 +2566,7 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix) } use_keepalive = KEEPALIVE_ALWAYS; execute_commands(commands, unpack_status, &si, - &push_options); + &push_options, &announced_oids); if (pack_lockfile) unlink_or_warn(pack_lockfile); sigchain_push(SIGPIPE, SIG_IGN); @@ -2591,6 +2603,7 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix) packet_flush(1); oid_array_clear(&shallow); oid_array_clear(&ref); + oidset_clear(&announced_oids); free((void *)push_cert_nonce); return 0; }