> On Mar 31, 2015, at 8:13 AM, Johan Corveleyn <jcor...@gmail.com> wrote: > >> On Tue, Mar 31, 2015 at 2:19 AM, Johan Corveleyn <jcor...@gmail.com> wrote: >>> On Sun, Mar 29, 2015 at 7:57 PM, Johan Corveleyn <jcor...@gmail.com> wrote: >>>> On Sat, Mar 28, 2015 at 5:09 PM, Bert Huijben <b...@qqmail.nl> wrote: >>>> >>>> >>>>> -----Original Message----- >>>>> From: Johan Corveleyn [mailto:jcor...@gmail.com] >>>>> Sent: vrijdag 27 maart 2015 22:03 >>>>> To: users@subversion.apache.org >>>>> Subject: Branching slow 1.8.11 https >>>>> >>>>> Does the following ring a bell for someone? >>>>> >>>>> Recently upgraded our server (on Solaris 10 SPARC) from 1.5.4 to >>>>> 1.8.11 (CollabNet package). Some time after that, we discovered that >>>>> branching was very slow. I'm talking about pure server-side branching >>>>> ('svn copy $URL/trunk $URL/branches/br1'). I'm testing with a 1.8.11 >>>>> client (tried both from same machine as the server, and from another >>>>> machine on the LAN (100 Mbit)). >>>>> >>>>> - Branching trunk (containing many directories and files): 6-8 minutes >>>>> - Branching a subfolder of trunk: 20-30 seconds (still very slow) >>>>> - Branching a single file is fast (< 0.5s or so). >>>>> >>>>> So it seems the performance degrades depending on the depth or size of the >>>>> tree. >>>>> >>>>> Now, it gets more interesting: >>>>> - The resulting rev file on the server is always very small (as it >>>>> should be, it contains only a lightweight 'copy' of the trunk node). >>>>> - Our repos is currently served via https (Apache 2.2.29). >>>>> - Branching with file:/// urls is fast (branching trunk takes 0.6s). >>>>> - When starting an svnserve instance serving the same repository, and >>>>> branching with svn:// urls, it's fast as well (also 0.6s). >>>>> - We reproduced it on a copy of the production repo. >>>>> - Experimenting with the test copy, we found that >>>>> $repos/dav/activities.d contains ~2000 files. When we clear that >>>>> directory, the branching times go down by more than half (~2 minutes >>>>> for trunk, ~10s for subdir of trunk --- i.e. still slow, but it >>>>> definitely has an impact). >>>>> - With a 1.7 client connecting with neon, the problem is the same. >>>>> - During the 'svn copy', an httpd child consumes a lot of cpu (around >>>>> half a core). >>>>> - There is no authz configured for this repo (SVNPathAuthz off). >>>>> - Backend is still in 1.5 format (we have not run svnadmin upgrade >>>>> yet, a dump+load is planned in a couple of weeks). >>>>> >>>>> So it seems clearly mod_dav_svn related (and not for instance related >>>>> to the FSFS backend). >>>>> >>>>> I don't think we have anything special in our httpd config: >>>>> [[[ >>>>> <Location /test_svn> >>>>> SVNInMemoryCacheSize 131072 >>>>> SVNCacheFullTexts on >>>>> SVNCacheTextDeltas on >>>>> SSLRequireSSL >>>>> AuthName "TEST Subversion Repository" >>>>> AuthType Basic >>>>> AuthBasicProvider ldap >>>>> AuthBasicAuthoritative off >>>>> AuthLDAPURL "ldap://redacted:389"; >>>>> AuthLDAPBindDN "redacted" >>>>> AuthLDAPBindPassword redacted >>>>> Require ldap-group redacted >>>>> DAV svn >>>>> SVNPath /path/to/test_repos >>>>> SVNPathAuthz off >>>>> </Location> >>>>> ]]] >>>>> >>>>> Any ideas? >>>>> Why the cpu usage by the server, what's it doing? >>>>> What is the dav/activities.d directory for? How come it contains so >>>>> many files? Is it ok to purge the old files from that directory? >>>> >>>> Httpd's mod_dav was updated in some recent version to do a full lock >>>> traversal on copies and moves. I think we already applied some >>>> optimizations, but the real fix would be that mod_dav shouldn't do this >>>> work (which our repos layer already does). >>>> >>>> I'm not sure which release we applied the first set of optimizations. >>> >>> Thanks for refreshing my memory. >>> >>> So the problem is known as issue #4531 (server-side copy (over dav) >>> uses too much memory) [1]. The memory usage issue has been fixed in >>> SVN 1.8.11 and 1.7.19 (see CHANGES), but a performance problem remains >>> (copy is no longer O(1), but depends on the size of the tree being >>> copied). That's a direct violation of one of Subversion's "old selling >>> points" vs. CVS: that branching / tagging is O(1). Branching / tagging >>> taking several minutes brings back "fond memories" from CVS' days. >>> >>> As Philip pointed out in his last comment on #4531 [2]: "This issue is >>> related to a change in mod_dav in 2.2.25 to fix PR54610 which >>> added a walk over the copy source looking for lock tokens." (also >>> released in 2.4.5; so both httpd 2.2.25+ and 2.4.5+ are affected -- >>> older httpd's won't have this problem I guess). >>> >>> Again quoting Philip: "Apache knows in advance that the walk is >>> redundant in cases such as Subversion's URL-to-URL copy but Subversion >>> cannot avoid the read access. We should attempt to fix mod_dav to >>> avoid the walk where possible." >>> >>> So my hope rests with Philip and others who might have the necessary >>> knowledge to fix this in mod_dav. It's really not acceptable that >>> branching / tagging (or I'm guessing also: moving a large tree with a >>> server-side move) takes several minutes. >>> >>> [1] http://subversion.tigris.org/issues/show_bug.cgi?id=4531 >>> [2] http://subversion.tigris.org/issues/show_bug.cgi?id=4531#desc12 >> >> I think I've found a workaround: it seems the tree walk by mod_dav is >> avoided when the request has a header Depth with value 0. I've tried >> adding >> >> <If "%{REQUEST_METHOD} == 'COPY'"> >> RequestHeader set Depth 0 >> </If> >> >> to the Location block of SVN, and the copy is fast again! And the good >> thing is: it's still a fully recursive copy :-) (otherwise it wouldn't >> be much of a workaround). >> >> 'svn copy' time for a very large tree (artificially generated with >> ~50000 folders and ~250000 files) is now down to 1,5 seconds (still >> three times slower than the same via file:/// or svn://, but good >> enough, and not O(sizeof(tree)) anymore). >> >> Is this workaround safe? Thoughts? >> It might even be something that can be exploited by our client, when >> 'svn copy'ing ... (though a "normal" server-side fix for this problem, >> within the normal workings of mod_dav, would of course be better >> still). > > Seems this workaround is pretty OK for now (apparently the subversion > code on the server ignores the Depth:0 for COPY requests, so the copy > is handled like a normal recursive copy). > > Bert suggested on irc to make the setting of the header also dependent > on the useragent string. > > For completeness: I'm now no longer seeing the 1,5 seconds time for > copying over dav. Today it's more like 0,5 - 0,7 seconds, i.e. the > same as with file:// and svn://. Maybe something was slowing down my > network temporarily yesterday evening. > > -- > Johan
Are we going to change the client to send this header? This seems like a very significant regression in our primary "promises" to allow it to wait for a mod_dav fix that might never even happen. Mark
