On Thu, Mar 05, 2009, thestar@xxxxxxxxxxxxxxxx wrote: > > The current git-p4 way of concatenating strings performs in O(n^2) > >and is therefore terribly slow with large files because of unnecessary > >memory copies. The following patch makes the operation O(n). > > The reason why it uses simple concatenation is to cut down on memory usage. > - It is a tradeoff. > > I think the modification you have made below is reasonable, however be > aware that memory usage could double, which substantially reduce the > size of the changesets that git-p4 would be able to import /at all/, > rather than to merely be slow. Uhm, no. The memory usage could be an additional X, where X is the size of the biggest file in the commit. Remember that commit() stores the complete commit data in memory before sending it to fast-import. Also, on my machine the extra memory is already used because at some point, "text += foo" calls realloc() anyway and often duplicates the memory used by text. The ideal solution is to use a generator and refactor the commit handling as a stream. I am working on that but it involves deeper changes, so as I am not sure it will be accepted, I'm providing the attached compromise patch first. At least it solves the appaling speed issue. I tuned it so that it never uses more than 32 MiB extra memory. Signed-off-by: Sam Hocevar <sam@xxxxxxx> --- contrib/fast-import/git-p4 | 10 +++++++++- 1 files changed, 9 insertions(+), 1 deletions(-) diff --git a/contrib/fast-import/git-p4 b/contrib/fast-import/git-p4 index 3832f60..151ae1c 100755 --- a/contrib/fast-import/git-p4 +++ b/contrib/fast-import/git-p4 @@ -984,11 +984,19 @@ class P4Sync(Command): while j < len(filedata): stat = filedata[j] j += 1 + data = [] text = '' while j < len(filedata) and filedata[j]['code'] in ('text', 'unicod e', 'binary'): - text += filedata[j]['data'] + data.append(filedata[j]['data']) del filedata[j]['data'] + # p4 sends 4k chunks, make sure we don't use more than 32 MiB + # of additional memory while rebuilding the file data. + if len(data) > 8192: + text += ''.join(data) + data = [] j += 1 + text += ''.join(data) + del data if not stat.has_key('depotFile'): sys.stderr.write("p4 print fails with: %s\n" % repr(stat)) -- Sam. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html