Domain_match_cache_size, domain_match_cache_timeout MTA option
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Domain match cache control (domain_match_cache_size, domain_match_cache_timeout)
As of JES MS 6.0, the domain_match_cache_size MTA option (as well as the domain_match_cache_timeout MTA option) is mostly irrelevant, since as of JES MS 6.0 there is an underlying domain map cache of domains. That is, the underlying domain lookup code used by the MTA as well as other Messaging Server components now maintains a (large) cache of lookup results; see the ldap_domain_timeout MTA option for a discussion of the timeout on the underlying domain lookup cache entries. The MTA's own private-to-the-MTA cache has thus become mostly redundant -- it's a cache in front of a cache (though its entries are smaller in the case of negative matches, so potentially if one was especially concerned about optimizing the case of caching of large numbers of negative matches, the MTA's private cache might be slightly useful).
The domain_match_cache_* options control some performance tuning formerly (in iMS 5.2) relevant when operating in direct LDAP mode, in particular when a rewrite rule with a $V in the template is being used. When such $V domain map lookups are performed, the results can be cached by the MTA (apart and in addition to the caching done by the underlying domain map LDAP lookup code); that is, an in memory cache is maintained by the MTA of the results of "recent" such lookups. The domain_match_cache_size MTA option, which defaults to 100000, controls how many results are cached. The domain_match_cache_timeout MTA option, which defaults to 600, specifies how long in seconds to maintain cache results. But note that all that's being cached here by the MTA is whether or not the domain is "local", (that is, in the DIT). The actual values of attributes, such as domainStatus, is cached in the underlying domain map code; see the ldap_domain_timeout MTA option for a discussion of the timeout for that underlying cache.
There is a trade-off between performance on the one hand, vs. memory usage and speed with which changes to the LDAP entries take effect on the other hand.
See also: MTA options, Option value syntax, Getting option changes to take effect, MTA options, listed alphabetically, MTA options, listed by functional groups, LDAP and URL lookup cache options, Direct LDAP domain lookup options, Direct LDAP lookups, ldap_domain_timeout MTA option, domain_match_cache_timeout MTA option, Rewrite rule $V LDAP lookup.
