On 21.11.2014 11:53, Philip Martin wrote: > [email protected] writes: > >> Author: philip >> Date: Thu Nov 20 22:36:27 2014 >> New Revision: 1640832 >> >> URL: http://svn.apache.org/r1640832 >> Log: >> Followup to r1618841, the old fast_memcpy() returned target+len but >> the replacement memcpy() returns target. >> >> * subversion/libsvn_delta/text_delta.c >> (patterning_copy): Adjust target after memcpy. > This bug caused checksum failures when reading a BDB repository. As far > as I can tell it only affects the BDB code (the delta combiner used in > the BDB code is the only place that generates svn_txdelta_target) and > this code is not exercised by the test suite. > > I don't understand the patterns that cause the repository to contain > svn_txdelta_target so I can't easily write a testcase.
The combiner only produces target copies if the source delta(s) contain them. We shouldn't be generating any since we started using the xdelta algorithm instead of vdelta; I don't really understand why BDB would be using vdelta instead, not even for compatibility reasons. In any case, your fix is correct. -- Brane P.S.: The presence of target copies in deltas could, in certain not-so-rare cases with overlapping target copies, make the delta combiner grind to a halt. The combiner algorithm could suddenly have a fourth-order dependency on the number of instructions, which would blow the CPU for the actual delta application sky-high. That's why dberlin replaced vdelta with xdelta, way back when.
