comparison mercurial/dirstate.py @ 45243:ad7006830106

dirstate: restore original estimation and update comment

The former comment didn't reflect the content of the dirstate entries,
the two nodes are a fixed header in the file and not per-entry. Split
the documented entry into the path part and the fixed header. The
heuristic itself is still valid, e.g. for the NetBSD src tree a maximum
path size of 142 and an average of 49, resulting in 66 bytes per entry
on average.

Differential Revision: https://phab.mercurial-scm.org/D8850

45242:5780a04a1b46

        if not st:
            return

        if util.safehasattr(parsers, b'dict_new_presized'):
            # Make an estimate of the number of files in the dirstate based on
            # its size. From a linear regression on a set of real-world repos,
            # all over 10,000 files, the size of a dirstate entry is 2 nodes
            # plus 45 bytes. The cost of resizing is significantly higher than the cost
            # of filling in a larger presized dict, so subtract 20% from the
            # size.
            #
            # This heuristic is imperfect in many ways, so in a future dirstate
            # format update it makes sense to just record the number of entries
            # on write.
            self._map = parsers.dict_new_presized(
                len(st) // ((2 * self._nodelen + 45) * 4 // 5)
            )

        # Python's garbage collector triggers a GC each time a certain number
        # of container objects (the number being defined by
        # gc.get_threshold()) are allocated. parse_dirstate creates a tuple
        # for each file in the dirstate. The C version then immediately marks

45243:ad7006830106

        if not st:
            return

        if util.safehasattr(parsers, b'dict_new_presized'):
            # Make an estimate of the number of files in the dirstate based on
            # its size. This trades wasting some memory for avoiding costly
            # resizes. Each entry have a prefix of 17 bytes followed by one or
            # two path names. Studies on various large-scale real-world repositories
            # found 54 bytes a reasonable upper limit for the average path names.
            # Copy entries are ignored for the sake of this estimate.
            self._map = parsers.dict_new_presized(len(st) // 71)

        # Python's garbage collector triggers a GC each time a certain number
        # of container objects (the number being defined by
        # gc.get_threshold()) are allocated. parse_dirstate creates a tuple
        # for each file in the dirstate. The C version then immediately marks