Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
Default constructed extremum_tracker has uninitialised _default_value
which basically makes it never correct to do that. Since this class is a
mechanism and not a value it doesn't really need to be a regular type,
so let's drop the default constructor.
Message-Id: <20190207162430.7460-1-pdziepak@scylladb.com>
extremum_tracker allows choosing a default value that's going to be used
only if no "real" values were provided. Since it is never compared with
the actual input values it can be anything. For instance, if the minimum
tracker default value is 0 and there was one update with the value 1 the
detected minimum is going to be 1 (the default is ignored).
However, this doesn't work when the trackers are merged since that
process always leaves the destination tracker in the "set" state
regardless whether any of the merged trakcers has ever seen any value.
This is fixed by this patch, by properly preserving _is_set state on
merge.
They will be re-used for collecting encoding statistics which is needed
to write SSTables 3.0.
Part of #1969.
Signed-off-by: Vladimir Krivopalov <vladimir@scylladb.com>
