Avoid quadratic checking of identity-constraints
key/unique/keyref schema attributes currently use qudratic loops
to check their various constraints (that keys are unique and that
keyrefs refer to existing keys). That becomes extremely slow if
there are many elements with keys. This happens in the wild with
e.g. the OVAL XML descriptions of security patches. You need the
openscap schemata, and then an example xml file:
% zypper in openscap-utils
% wget ftp://ftp.suse.com/pub/projects/security/oval/opensuse.leap.15.1.xml
% time xmllint --schema /usr/share/openscap/schemas/oval/5.5/oval-definitions-schema.xsd opensuse.leap.15.1.xml > /dev/null
opensuse.leap.15.1.xml validates
real 16m59,857s
user 16m55,787s
sys 0m1,060s
This patch makes libxml use a hash table to avoid the quadratic
behaviour. The existing hash table only accepts strings as keys, so
we're mostly reusing the canonical representation of key values to derive
such strings (with the caveat given in a comment). The alternative
would be to rework the hash table code to accept either numbers or free
functions as hash workers, but the code is fast enough as is.
With the patch we have this then:
% time LD_LIBRARY_PATH=./libxml2/.libs/ ./libxml2/.libs/xmllint --schema /usr/share/openscap/schemas/oval/5.5/oval-definitions-schema.xsd opensuse.leap.15.1.xml > /dev/null
opensuse.leap.15.1.xml validates
real 0m3,531s
user 0m3,427s
sys 0m0,103s
So, a ~300x speedup. This patch survives 'make check' and 'make tests'.
1 file changed
