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
