cache_storage_api.h contains pure C declarations, while
cache_storage_api.hh contains C++ declarations. Functions dealing
with CACHE_KEY moved to these headers.
Initial POC implementation that is capable of outputting the
rules of the cache.
In order to do that conveniently, the json object is retained for
the lifetime of the CACHE_RULES object.
MXS-848 (partially). The QLA-filter now has additional options
to control the printing.
1. "append"
This toggles append-mode, where the filter opens the log files in
update mode (if file already existed) and only adds text to the end.
2. "print_service"
This toggles writing the service name onto each row. Mostly useful
with the unified_file-setting.
3. "print_session"
This toggles writing the session number onto each row. Mostly useful
with the unified_file-setting.
Also, the filter now writes a header to the beginning of the file
when creating it.
The printing has been separated to its own helper-function, in case
more accurate control will be added in the future.
The code prevented scaling by imposing global spinlocks for the DCBs and
SESSIONs. Removing this list means that a thread-local list must be taken
into use to replace it.
Unnecessary methods were also removed from CachePT and CacheMT
as it does not make sense to create more than one single instance
of those per filter instance. Consequently there is no need for
them to be able to use an existing StorageFactory (and CacheRules).
The maximum count and maximum size of the cache can now be
specified and a storage can declare what capabilities it has.
If a storage modile cannot enforce the maximum count or maximum
size limits, the storage is decorated with an LRU storage that
can.
The LRUStorage hierarchy implements the decorator pattern and
is capable of providing LRU behaviour to any underlying storage.
There are two concrete classes - LRUStorageST and LRUStorageMT -
that can be used in single thread and multiple thread contentx,
respectively.
Also tests the convention of placing _ as suffix on member
variables.
The query throttling functionality was broken by the move to the per
thread rule system. One way to fix this is to move the session specific
throttling information into the client session itself. This allows for a
simpler system with no direct dependencies on the rules or users
themselves.
Storage is now abstract with StorageReal (that uses an actual
storage module) derived from it. This to prepare for a stackable
case where LRU behaviour is implemented in front of the actual
physcal storage.
The per thread cache is implemented so that there is one single
thread cache per thread.
This uses shared_ptr, which is available in different places
depending on which GCC version is default on the target platform.
So, before this is merged to develop, that needs to be sorted out.
A simple cache is one that does not transparently use multiple
storages in the background. That will be the case when a separate
cache per thread is used. Both CacheST and CacheMT are now derived
from CacheSimple.
A fair amount of what used to be in Cache has now been moved to
CacheSimple. What remains is what surely is common for all cache
types.
Now the basic structure is in place:
- cachefilter.cc is the MaxScale filter interface.
- Cache is the actual cache class that will also handle LRU issues.
- SessionCache (sessioncache.cc) is the session specific cache class
that using Cache acts as the cache for a particular session.
If an item is stale, then one SessionCache will update it.
- StorageFactory is the component that is capable of loading a module
providing storage facilities.
- Storage is the actual key/value store.
