dev-db/postgresql-server/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
<herd>postgresql</herd>
<use>
  <flag name='uuid'>Enable server side UUID generation
    (via <pkg>dev-libs/ossp-uuid</pkg>)</flag>
  <flag name='pg_legacytimestamp'>Use double precision floating-point numbers
    instead of 64-bit integers for timestamp storage.
  </flag>
</use>
</pkgmetadata>