Ensure that the size of the cache is never bigger than the "max_size".
Before this patch the size of the cache could have been indefinitely bigger than
the requested value during the refresh time period which is clearly an undesirable
behaviour.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Sometimes we don't want the cached values to be periodically reloaded.
This patch adds the ability to control this using a ReloadEnabled template parameter.
In case the reloading is not needed the "loading" function is not given to the constructor
but rather to the get_ptr(key, loader) method (currently it's the only method that is used, we may add
the corresponding get(key, loader) method in the future when needed).
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Current get(...) interface restricts the cache to work only with copy-constructable
values (it returns future<Tp>).
To make it able to work with non-copyable value we need to introduce an interface that would
return something like a reference to the cached value (like regular containers do).
We can't return future<Tp&> since the caller would have to ensure somehow that the underlying
value is still alive. The much more safe and easy-to-use way would be to return a shared_ptr-like
pointer to that value.
"Luckily" to us we value we actually store in a cache is already wrapped into the lw_shared_ptr
and we may simply return an object that impersonates itself as a smart_pointer<Tp> value while
it keeps a "reference" to an object stored in the cache.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Allow a variable entry size parameter.
Provide an EntrySize functor that would return a size for a
specific entry.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Get rid of the "proprietary" solution for asynchronous values on-demand loading.
Use utils::loading_shared_values instead.
We would still need to maintain intrusive set and list for efficient shrink and invalidate
operations but their entry is not going to contain the actual key and value anymore
but rather a loading_shared_values::entry_ptr which is essentially a shared pointer to a key-value
pair value.
In general, we added another level of dereferencing in order to get the key value but since
we use the bi::store_hash<true> in the hook and the bi::compare_hash<true> in the bi::unordered_set
this should not translate into an additional set lookup latency.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
The timer is armed inside the section guarded by the _timer_reads_gate
therefore it has to be canceled after the gate is closed.
Otherwise we may end up with the armed timer after stop() method has
returned a ready future.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Message-Id: <1501603059-32515-1-git-send-email-vladz@scylladb.com>
loading_cache invokes a timer that may issue asynchronous operations
(queries) that would end with writing into the internal fields.
We have to ensure that these operations are over before we can destroy
the loading_cache object.
Fixes#2624
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Message-Id: <1501096256-10949-1-git-send-email-vladz@scylladb.com>
Arm the timer with a period that is not greater than either the permissions_validity_in_ms
or the permissions_update_interval_in_ms in order to ensure that we are not stuck with
the values older than permissions_validity_in_ms.
Fixes#2590
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Fix the shrink() O(n log n) complexity issue by constantly pushing the corresponding intrusive
list entry to the head of the list every time the values are read.
This will keep the list ordered by the last read time from the most recently read
to the least recently read entry.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
- Start the cache with 256 buckets - the minimum number of buckets.
- Limit the maximal number of buckets by 1M buckets.
- Keep the load factor between 0.25 and 1.0 as long as the number of buckets is
between the minimum and the maximum values mentioned above.
- Grow and shrink the hash every "refresh" period if needed.
- Enable bi::power_2_buckets and bi::compare_hash bi::unordered_set options.
- Enable bi::unordered_set_base_hook's bi::store_hash option.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Make the underlying map to be a boost::intrusive::unordered_set<timestamped_val>
instead of std::unordered_set<Key, timestamped_val>.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
According to description of permissions_validity_in_ms the permissions_cache is enabled if this
value is set to a non-zero value. Otherwise the permissions_cache is disabled.
According to the permissions_update_interval_in_ms description it must have a non-zero value if permissions_cache
is enabled.
permissions_cache_max_entries description doesn't explicitly state it but it makes no sense to allow it to be zero
if permissions_cache is enabled.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
This patch changes the way a loading_cache works.
Before this patch:
1) If a permissions key is not in the cache it's loaded in the foreground and the original
query is blocked till the permissions are loaded.
2) Every _period the timer does the following:
1) If a value was loaded more than _expiry time ago it is removed from the cache.
2) If the cache is too big - the less recently loaded values are removed till the cache
fits the requested size.
After this patch:
1) If a permissions key is not in the cache it's loaded in the foreground and the original
query is blocked till the permissions are loaded.
2) Every _period the timer does the following:
1) If a value in the cache was loaded or read for the last time more than _expiry time ago - it's removed from the cache.
2) If the cache is too big - the less recently read values are removed till the cache fits the requested size.
3) The values that were loaded more than _refresh time ago are re-read in the background.
The new implementation allows to minimize the amount of the foreground reads for a frequently used value to a single
event (when the value is loaded for the first time).
It also ensures we do not reload values we no longer need.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
