Nadav Har'El f84094320d exceptions: de-inline exception constructors ...

The header file "exceptions/exceptions.hh" and the exception types in it
is used by virtually every source file in Scylla, so excessive includes
and templated code generation in this header could slow down the build
considerably.

Before this patch, all of the exceptions' constructors were inline in
exceptions.hh, so source file using one of these exceptions will need
to recompile the code, which is fairly heavy, using the fmt templates
for various types. According to ClangBuildAnalyzer, 323 source files
needed to materialize prepare_message<db::consistency_level,int&,int&>,
taking 0.3 seconds each.

So this patch moves the exception constructors from the header file
exceptions.hh to the source file exceptions.cc. The header file no longer
uses fmt.

Unfortunately, the actual build-time savings from this patch is tiny -
around 0.1%... It turns out that most of the prepare_message<>
compilation time comes from fmt compilation time, and since virtually
all source files use fmt for other header reasons (intentionally or
through other headers), no compilation time can be saved. Nevertheless,
I hope that as we proceed with more cleanups like this and eliminate
more unnecessary code-generation-in-headers, we'll start seeing build
time drop.

Signed-off-by: Nadav Har'El <nyh@scylladb.com>

2022-02-28 14:47:41 +02:00

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