This adds indirection of large version vectors in the same manner as we
already to block lists. The effect is the same: less duplicated data in
some situations.
To mitigate the impact for when this indirection
wouldn't be needed I've added an indirection cutoff for both blocks and
the new version vector stuff: we don't do the indirection at all for
small block lists or small version vectors, instead storing it directly
like we used to do. This is faster for small files and small setups.
Storing assets as []byte requires every compiled-in asset to be copied
into writable memory at program startup. That currently takes up 1.6MB
per syncthing process. Strings stay in the RODATA section and should be
shared between processes running the same binary.
This makes version vector values clock based instead of just incremented
from zero. The effect is that a vector that is created from scratch
(after database reset) will have a higher value for the local device
than what it could have been previously, causing a conflict. That is, if
we are A and we had
{A: 42, B: 12}
in the old scheme, a reset and rescan would give us
{A: 1}
which is a strict ancestor of the older file (this might be wrong). With
the new scheme we would instead have
{A: someClockTime, b: otherClockTime}
and the new version after reset would become
{A: someClockTime+delta}
which is in conflict with the previous entry (better).
In case the clocks are wrong (current time is less than the value in the
vector) we fall back to just simple increment like today.
This scheme is ineffective if we suffer a database reset while at the
same time setting the clock back far into the past. It's however no
worse than what we already do.
This loses the ability to emit the "added" event, as we can't look for
the magic 1 entry any more. That event was however already broken
(#5541).
Another place where we infer meaning from the vector itself is in
receive only folders, but there the only criteria is that the vector is
one item long and includes just ourselves, which remains the case with
this change.
* wip
This changes the build script to build all the things in one go
invocation, instead of one invocation per cmd. This is a lot faster
because it means more things get compiled concurrently. It's especially
a lot faster when things *don't* need to be rebuilt, possibly because it
only needs to build the dependency map and such once instead of once per
binary.
In order for this to work we need to be able to pass the same ldflags to
all the binaries. This means we can't set the program name with an
ldflag.
When it needs to rebuild everything (go clean -cache):
( ./old-build -gocmd go1.14.2 build all 2> /dev/null; ) 65.82s user 11.28s system 574% cpu 13.409 total
( ./new-build -gocmd go1.14.2 build all 2> /dev/null; ) 63.26s user 7.12s system 1220% cpu 5.766 total
On a subsequent run (nothing to build, just link the binaries):
( ./old-build -gocmd go1.14.2 build all 2> /dev/null; ) 26.58s user 7.53s system 582% cpu 5.853 total
( ./new-build -gocmd go1.14.2 build all 2> /dev/null; ) 18.66s user 2.45s system 1090% cpu 1.935 total
This makes the GC runner a service that will stop fairly quickly when
told to.
As a bonus, STTRACE=app will print the service tree on the way out,
including any errors they've flagged.
So, in a funny plot twist, it turns out that WriteFile in Go 1.13
doesn't actually set the read only bit on Windows when called with
permissions 0444 so my test was broken. With an improved test it turns
out that Rename does not, in fact, overwrite a read-only file on
Windows. This adds a fix for that.
(Rename might get improved in Go 1.15...)
