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
hg --debug init
echo this is a1 > a
hg add a
hg commit -m0 -d "1000000 0"
echo this is b1 > b
hg add b
hg commit -m1 -d "1000000 0"
hg manifest --debug 1
echo this is c1 > c
hg rawcommit -p 1 -d "1000000 0" -m2 c
hg manifest --debug 2
hg -v parents
rm b
hg rawcommit -p 2 -d "1000000 0" -m3 b
hg manifest --debug 3
hg -v parents
echo this is a22 > a
hg rawcommit -p 3 -d "1000000 0" -m4 a
hg manifest --debug 4
hg -v parents
echo this is c22 > c
hg rawcommit -p 1 -d "1000000 0" -m5 c
hg manifest --debug 5
hg -v parents
# merge, but no files changed
hg rawcommit -p 4 -p 5 -d "1000000 0" -m6
hg manifest --debug 6
hg -v parents
# no changes what-so-ever
hg rawcommit -p 6 -d "1000000 0" -m7
hg manifest --debug 7
hg -v parents