Implement simple LDAP cache layer

Insert a class before LDAPClient to cache the return value
of get_entry() and certain exceptions (NotFound and
EmptyResult). The cache uses an OrderedDict for the cases
where a large cache might result an LRU model can be used.

The cache be enabled (default) or disabled using
ldap_cache=True/False.

This cache is per-request so is not expected to grow
particularly large except in the case of a large batch
command.

The key to the cache entry is the dn of the object
being requested.

Any write to or referencing a cached dn is evicted from
the cache.

The set of attributes is somewhat taken into consideration.
"*" does not always match everything being asked for by
a plugin so unless the requested set of attributes is a
direct subset of what is cached it will be re-fetched. Err
on the side of safety.

Despite this rather conserative approach to caching 29%
of queries are saved with ipatests/xmlrpc_tests/*

https://pagure.io/freeipa/issue/8798

Signed-off-by: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Rafael Guterres Jeffman <rjeffman@redhat.com>

ipapython/ipaldap.py

@@ -31,6 +31,8 @@ import os
 import pwd
 import warnings
 
+from collections import OrderedDict
+
 from cryptography import x509 as crypto_x509
 from cryptography.hazmat.primitives import serialization
 
@@ -47,7 +49,7 @@ from ipalib.constants import LDAP_GENERALIZED_TIME_FORMAT
 # pylint: enable=ipa-forbidden-import
 from ipaplatform.paths import paths
 from ipapython.ipautil import format_netloc, CIDict
-from ipapython.dn import DN
+from ipapython.dn import DN, RDN
 from ipapython.dnsutil import DNSName
 from ipapython.kerberos import Principal
 
@@ -1698,6 +1700,7 @@ class LDAPClient:
         modlist = entry.generate_modlist()
         if not modlist:
             raise errors.EmptyModlist()
+        logger.debug("update_entry modlist %s", modlist)
 
         # pass arguments to python-ldap
         with self.error_handler():
@@ -1749,3 +1752,237 @@ def get_ldap_uri(host='', port=389, cacert=None, ldapi=False, realm=None,
             return 'ldap://%s' % format_netloc(host, port)
         else:
             raise ValueError('Protocol %r not supported' % protocol)
+
+
+class CacheEntry:
+    def __init__(self, entry=None, attrs_list=None, exception=None,
+                 get_effective_rights=False, all=False):
+        self.entry = entry
+        self.attrs_list = attrs_list
+        self.exception = exception
+        self.all = all
+
+
+class LDAPCache(LDAPClient):
+    """A very basic LRU Cache using an OrderedDict"""
+
+    def __init__(self, ldap_uri, start_tls=False, force_schema_updates=False,
+                 no_schema=False, decode_attrs=True, cacert=None,
+                 sasl_nocanon=True, enable_cache=True, cache_size=100):
+
+        self.cache = OrderedDict()
+        self._enable_cache = True  # initialize to zero to satisfy pylint
+
+        object.__setattr__(self, '_cache_misses', 0)
+        object.__setattr__(self, '_cache_hits', 0)
+        object.__setattr__(self, '_enable_cache',
+                           enable_cache and cache_size > 0)
+        object.__setattr__(self, '_cache_size', cache_size)
+
+        super(LDAPCache, self).__init__(
+            ldap_uri, start_tls, force_schema_updates, no_schema,
+            decode_attrs, cacert, sasl_nocanon
+        )
+
+    @property
+    def hit(self):
+        return self._cache_hits  # pylint: disable=no-member
+
+    @property
+    def miss(self):
+        return self._cache_misses  # pylint: disable=no-member
+
+    @property
+    def max_entries(self):
+        return self._cache_size  # pylint: disable=no-member
+
+    def emit(self, msg, *args, **kwargs):
+        if self._enable_cache:
+            logger.debug(msg, *args, **kwargs)
+
+    def add_cache_entry(self, dn, attrs_list=None, get_all=False,
+                        entry=None, exception=None):
+        # idnsname - caching prevents delete when mod value to None
+        # cospriority - in a Class of Service object, uncacheable
+        # TODO - usercertificate was banned at one point and I don't remember
+        #        why...
+        BANNED_ATTRS = {'idnsname', 'cospriority'}
+        if not self._enable_cache:
+            return
+
+        self.remove_cache_entry(dn)
+
+        if (
+            DN('cn=config') in dn
+            or DN('cn=kerberos') in dn
+            or DN('o=ipaca') in dn
+        ):
+            return
+
+        if exception:
+            self.emit("EXC: Caching exception %s", exception)
+            self.cache[dn] = CacheEntry(exception=exception)
+        else:
+            if not BANNED_ATTRS.intersection(attrs_list):
+                self.cache[dn] = CacheEntry(
+                    entry=entry.copy(),
+                    attrs_list=deepcopy(attrs_list),
+                    all=get_all,
+                )
+            else:
+                return
+
+        self.cache.move_to_end(dn)
+
+        if len(self.cache) > self.max_entries:
+            (dn, entry) = self.cache.popitem(last=False)
+            self.emit("LRU: removed %s", dn)
+
+    def clear_cache(self):
+        self.cache_status('FINAL')
+        object.__setattr__(self, 'cache', OrderedDict())
+        object.__setattr__(self, '_cache_hits', 0)
+        object.__setattr__(self, '_cache_misses', 0)
+
+    def cache_status(self, type):
+        self.emit("%s: Hits %d Misses %d Size %d",
+                  type, self.hit, self.miss, len(self.cache))
+
+    def remove_cache_entry(self, dn):
+        assert isinstance(dn, DN)
+        self.emit('DROP: %s', dn)
+        if dn in self.cache:
+            del self.cache[dn]
+        else:
+            self.emit('DROP: not in cache %s', dn)
+
+    #  Begin LDAPClient methods
+
+    def add_entry(self, entry):
+        self.emit('add_entry')
+        self.remove_cache_entry(entry.dn)
+        super(LDAPCache, self).add_entry(entry)
+
+    def update_entry(self, entry):
+        self.emit('update_entry')
+        self.remove_cache_entry(entry.dn)
+        super(LDAPCache, self).update_entry(entry)
+
+    def delete_entry(self, entry_or_dn):
+        self.emit('delete_entry')
+        if isinstance(entry_or_dn, DN):
+            dn = entry_or_dn
+        else:
+            dn = entry_or_dn.dn
+
+        self.remove_cache_entry(dn)
+
+        super(LDAPCache, self).delete_entry(dn)
+
+    def move_entry(self, dn, new_dn, del_old=True):
+        self.emit('move_entry')
+        self.remove_cache_entry(dn)
+        self.remove_cache_entry(new_dn)
+
+        super(LDAPCache, self).move_entry(dn, new_dn, del_old)
+
+    def modify_s(self, dn, modlist):
+        self.emit('modify_s')
+        if not isinstance(dn, DN):
+            dn = DN(dn)
+
+        self.emit('modlist %s', modlist)
+        for (_op, attr, mod_dn) in modlist:
+            if attr.lower() in ('member',
+                                'ipaallowedtoperform_write_keys',
+                                'managedby_host'):
+                for d in mod_dn:
+                    if not isinstance(d, (DN, RDN)):
+                        d = DN(d.decode('utf-8'))
+                        self.emit('modify_s %s', d)
+                        self.remove_cache_entry(d)
+
+        self.emit('modify_s %s', dn)
+        self.remove_cache_entry(dn)
+
+        return super(LDAPCache, self).modify_s(dn, modlist)
+
+    def get_entry(self, dn, attrs_list=None, time_limit=None,
+                  size_limit=None, get_effective_rights=False):
+        # pylint: disable=no-member
+        if not self._enable_cache:
+            return super(LDAPCache, self).get_entry(
+                dn, attrs_list, time_limit, size_limit, get_effective_rights
+            )
+        self.emit("Cache lookup: %s", dn)
+
+        entry = self.cache.get(dn)
+        if get_effective_rights and entry:
+            # We don't cache this so do the query but don't drop the
+            # entry.
+            entry = None
+
+        if entry and entry.exception:
+            hits = self._cache_hits + 1  # pylint: disable=no-member
+            object.__setattr__(self, '_cache_hits', hits)
+            self.emit("HIT: Re-raising %s", entry.exception)
+            self.cache_status('HIT')
+            raise entry.exception
+
+        self.emit("Requested attrs_list %s", attrs_list)
+        if entry:
+            self.emit("Cached attrs_list %s", entry.attrs_list)
+
+        if not attrs_list:
+            attrs_list = ['*']
+        elif attrs_list == ['']:
+            attrs_list = ['dn']
+
+        get_all = False
+        if (
+            entry
+            and (attrs_list in (['*'], ['']))
+            and (entry.attrs_list in (['*'], ['']))
+        ):
+            get_all = True
+
+        if entry and entry.all and get_all:
+            # self.hit  # pylint: disable=pointless-statement
+            hits = self._cache_hits + 1  # pylint: disable=no-member
+            object.__setattr__(self, '_cache_hits', hits)
+            self.cache_status('HIT')
+            return entry.entry
+
+        # Be sure we have all the requested attributes before returning
+        # a cached entry.
+        if entry and attrs_list:
+            req_attrs = set(attr.lower() for attr in set(attrs_list))
+            cache_attrs = set(attr.lower() for attr in entry.attrs_list)
+            if (req_attrs.issubset(cache_attrs)):
+                hits = self._cache_hits + 1  # pylint: disable=no-member
+                object.__setattr__(self, '_cache_hits', hits)
+                self.cache_status('HIT')
+                return entry.entry
+
+        try:
+            entry = super(LDAPCache, self).get_entry(
+                dn, attrs_list, time_limit, size_limit, get_effective_rights
+            )
+        except (errors.NotFound, errors.EmptyResult) as e:
+            # only cache these exceptions
+            self.add_cache_entry(dn, exception=e)
+            misses = self._cache_misses + 1  # pylint: disable=no-member
+            object.__setattr__(self, '_cache_misses', misses)
+            self.cache_status('MISS: %s' % e)
+            raise
+        # pylint: disable=try-except-raise
+        except Exception:
+            # re-raise anything we aren't caching
+            raise
+        else:
+            self.add_cache_entry(dn, attrs_list=attrs_list, get_all=get_all,
+                                 entry=entry)
+        misses = self._cache_misses + 1  # pylint: disable=no-member
+        object.__setattr__(self, '_cache_misses', misses)
+        self.cache_status('MISS')
+        return entry