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
# initial
hg init test-a
cd test-a
cat >test.txt <<"EOF"
1
2
3
EOF
hg add test.txt
hg commit -m "Initial" -d "1000000 0"
# clone
cd ..
hg clone test-a test-b
# change test-a
cd test-a
cat >test.txt <<"EOF"
one
two
three
EOF
hg commit -m "Numbers as words" -d "1000000 0"
# change test-b
cd ../test-b
cat >test.txt <<"EOF"
1
2.5
3
EOF
hg commit -m "2 -> 2.5" -d "1000000 0"
# now pull and merge from test-a
hg pull ../test-a
hg merge
# resolve conflict
cat >test.txt <<"EOF"
one
two-point-five
three
EOF
rm -f *.orig
hg commit -m "Merge 1" -d "1000000 0"
# change test-a again
cd ../test-a
cat >test.txt <<"EOF"
one
two-point-one
three
EOF
hg commit -m "two -> two-point-one" -d "1000000 0"
# pull and merge from test-a again
cd ../test-b
hg pull ../test-a
hg merge --debug
cat test.txt
hg debugindex .hg/store/data/test.txt.i
hg log