revlog: break up compression of large deltas
Python's zlib apparently makes an internal copy of strings passed to
compress(). To avoid this, compress strings 1M at a time, then join
them at the end if the result would be smaller than the original.
For initial commits of large but compressible files, this cuts peak
memory usage nearly in half.
#!/bin/sh
# In the merge below, the file "foo" has the same contents in both
# parents, but if we look at the file-level history, we'll notice that
# the version in p1 is an ancestor of the version in p2. This test
# makes sure that we'll use the version from p2 in the manifest of the
# merge revision.
hg init repo
cd repo
echo foo > foo
hg ci -d '0 0' -qAm 'add foo'
echo bar >> foo
hg ci -d '0 0' -m 'change foo'
hg backout -d '0 0' -r tip -m 'backout changed foo'
hg up -C 0
touch bar
hg ci -d '0 0' -qAm 'add bar'
hg merge --debug
hg debugstate | grep foo
hg st -A foo
hg ci -d '0 0' -m 'merge'
hg manifest --debug | grep foo
hg debugindex .hg/store/data/foo.i