The SwappyItems Store is a flexible c++17 multicore single disk key-value storage. If the data in RAM gets large, it behaves similar to your system swap, but with more parameters and it swaps only the data - not the program code!

Main difference to other key-value stores:

Buckets with Bloom-filter instead of B*-tree or Log-structured merge-tree (LSM)
posibility of persistance and breakpoints
not RAM only, not DISK only
very flexible in data: value is not just "String"
not focused on multible disks or networking
flat: no need of a fat framework (just include SwappyItems.hpp)
no additional libs!
not all keys are stored in RAM: SwappyItems uses min/max and bloomfilter to search keys in files
modern c++17 build-in multicore usage
modern c++11 lambda expression API

Go to the Documentation of SwappyItems or take a look to the SwappyItems Source Code.

Examples

Only the examples (see Makefile) need -lz -losmpbf -lprotobuf (additional libs) for phrasing OSM data.

ToDo (nice to have)

implement a larger code version with PriorityQueue (for a minimal spanning tree use-case)
make number of items in swapped files variable with additional focus on real RAM usage, and ...
Because the vector<key> data can be very big, SwappyItems should additionally swap data from RAM to DISK, if to many items and vector elements are in RAM.
Implement a bucket based Priority Queue or building parallel processing winner trees in PriorityQueue heap. Idea for buckets: onion-like with two SwappyItems stores. Use key as a prio bucket and vector<key> with all keys with same prio. These keys are the keys from the 2nd SwappyItems Store, where the original data items is stored.
split writing into files (a swap event makes some sorted file buckets) in multiple threads
do prefetching in PriorityQueue for next to actual min prio Items
minimal spanning tree example code

SwappyQueue

I try to implement a 2 phase pairing heap on the head of SwappyItems.
testing with netbeans8.2 dev (2018) in examples/SwappyQueueTest/ folder
still with bugs :-(

SwappyItems: API basics

(constructor)

It trys to SwappyItems::wakeup() from hibernate files. The id parameter identifies the SwappyItems Store (important for the DISK/swap path!).

(destructor)

Makes a SwappyItems::hibernate() from RAM to DISK.

bool = set(key, value)

Set or create an item. It returns false, if the item is created (and not overwritten).

bool = set(key, value, vector<keys>)

Set or create an item. It returns false, if the item is created (and not overwritten). You can add a vector with additional keys in it.

pair(value, vector<keys>) * = get(key)

Get the value by key. You get a pointer to that data pair. If it does not exist, you get a nullptr.

del(key)

Delete a item.

min() and max()

Get the smallest or the biggest key in the SwappyItems Store.

getStatistic()

You get a SwappyItems::statistic_s with many values (inserts, sizes, deletes, lookup failures, ...) to deploy the SwappyItems Store.

bool = each(back, lambda func)

iterate through all elements at a fixed state
with a lambda function it is similar to a "find" (if lambda returns true, the each() breaks)
can change data via lambda
gives a reference back to last processed data
returns false if the loop did not break and iterated through all items

bool = apply(back, key, lambda func)

It is usable with a lambda function and similar to SwappyItems::get() and SwappyItems::set(). It does not change the swap data and behavior and thus this access it a bit slow. If you want to get or change data in the same SwappyItems store, where you iter through with SwappyItems::each(), then you must use SwappyItems::apply() in the lambda function of SwappyItems::each(). It returns false if the item does not exit.