Ouroboros

Embedded NoSQL storage of data. This storage can use like round-robin database. Ouroboros aims to handle time series data such as sensors values, network bandwidth, temperatures or CPU load. The data is stored in a circular buffer based database, thus the system storage footprint remains constant over time. This storage stores data in a data table that has some depth and if number of records over the depth, the new record overwrites the oldest record.

Help

Ouroboros provides access to a dataset that has a set of tables. In one dataset, tables have the same record structure and the same maximum number of records (the same depth). Access to a table is provided by key.

Fields

The following field type are supported:

• FIELD_FLOAT.
• FIELD_DOUBLE.
• FIELD_UINT8.
• FIELD_UINT16.
• FIELD_UINT32.
• FIELD_UINT64.
• FIELD_INT8.
• FIELD_INT16.
• FIELD_INT32.
• FIELD_INT64.
• FIELD_STRING.

Record

If you want to use records that should have, for example, 3 fields, you should use the following type of record:

typedef record3<FIELD_UINT32, FIELD_DOUBLE, FIELD_UINT8> record_type;

Index

Records of a table can be indexed by single field.

• index_null determines that the record doesn't have an indexed field.
• index1 determines that the record has an index by the first field.
• index2 determines that the record has an index by the second field.
• etc.

Key

The type of key determines where the table stores its indexes. The two types of key are supported:

• simple_key determines the table stores its indexes in memory.
• tree_key determines the table stores its indexes in itself.

Interface

Type of interface determines the behavior of a dataset. The two interface type are supported:

• local_interface determines the dataset coud be used by a single process.
• shared_interface determines the dataset coud be used by several processes.

Dataset

The dataset determines the number of tables stored and their depth. For example, following data set has 10 tables that can store 1000 records:

typedef dataset<simple_key, record_type, index_null, shared_interface> dataset_type;
dataset_type dataset("dbname", 10, 1000);

Session

Session provides access to a table. A dataset has two types of session:

• session_rd this session can provide only read operations.
• session_wr this session can provide read and write operations.

Session of one table can't influnce to a session of another table, but there are the following rules for sessions of one tables:

• If there is an active session_rd, you can open several new session_rds, but you can't open any sessions_wrs.
• If there is an active session_wr, you can't open any new session_rds and any sessions_wrs.

Thus for a single table, read operations can be handled at one time but active write operations can be only one at one time.

For example, the following code works with a table that has a key equal to 0, and first gets count of stored records and then gets their:

{
    dataset_type::serssion_rd session_rd = dataset.session_rd(0);
    const size_t count = session_rd->count();
    dataset_type::records_list records(count);
    session_rd->read_front(records);
}

Thus, a session restricts access to a single table in a dataset. If there will be some exception when you use some kind of session, then all changes made by the session will be discarded.

Transaction

Transaction, unlike a session, allows to lock the entire dataset. If there will be some exception when you use some transaction, then all changes made by the transaction will be discarded. For example, if we need to add the new table:

{
    typedef transaction<dataset_type> transaction_type;
    transaction_type transaction(dataset);
    if (!dataset.table_exists(0))
    {
    	dataset.add_table(0);
    }
}

Examples

This project has several examples, you can see them here: examples/ :)

License

MIT License

Copyright (c) 2019 Mikhail Belyaev

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.