Dear all, The forthcoming version of NaviServer will support transaction semantics for ns_cache.
Background: when ns_cache_* commands are used within DB transactions (e.g. in OpenACS), it might occur, that partial results of the transaction are cached before the transaction is committed. When the transaction is rolled back, invalid values might be kept in the cache leading to erroneous and hard to debug behavior. Furthermore, information about committed changes might leak into other threads via the cache. The new cache transaction semantics is implemented via the three new commands ns_cache_transaction_begin ns_cache_transaction_commit ns_cache_transaction_rollback When no ns_cache_transaction* command is used, the behavior is exactly as before. When cache transactions are used (initiated by a ns_cache_transaction_begin and ended via ns_cache_transaction_commit or ns_cache_transaction_rollback, the ns_cache commands provide in essence the following functionalities: a) The ability to rollback of the values since the matching ns_cache_transaction_begin b) Isolation of behavior: cached values from incomplete cache transactions are just visible from the current thread, but not from other threads. c) Nesting: transactions can be nested (up to a compile time constant, currently 16) d) Introspection: the statistics about cache commits and rollbacks are included in the cache statistics. Implementation: The implementation is an extension of the pre-existing update semantics and follows as close as possible the existing model used in ns_cache_eval. The "value" of a cache entry is NULL until a commit is performed, other threads competing for the same cache entry have to wait for the "commit" operations. The old C-API continues to work as before. The new transaction aware interface is implemented over the following C functions Ns_CacheFindEntryT() Ns_CacheFirstEntryT() Ns_CacheGetValueT() Ns_CacheNextEntryT() Ns_CacheWaitCreateEntryT() In order to avoid potential unwanted long-time locks on cache entries when cache transactions are not properly closed (e.g. in error cases), "ns_cleanup" is now extended to roll back all changes. The following ns_cache commands are now cache transaction aware: ns_cache_get ns_cache_eval ns_cache_incr ns_cache_append ns_cache_lappend ns_cache_keys ns_cache_flush All the best -gn ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ naviserver-devel mailing list naviserver-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/naviserver-devel
