compaction: Enable filtering reader only on behalf of cleanup compaction
compaction: Enable filtering reader only on behalf of cleanup compaction

After 13fa2bec4c11859b5, every compaction will be performed through a filtering
reader because consumers cannot do the filtering if interposer consumer is
enabled.

It turns out that filtering_reader is adding significant overhead when regular
compactions are running. As no other compaction type need to actually do
any filtering, let's limit filtering_reader to cleanup compaction.
Alternatively, we could disable interposer consumer on behalf of cleanup,
or add support for the consumers to do the filtering themselves but that
would add lots of complexity.

Fixes #7748.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>
Message-Id: <20201230194516.848347-2-1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla