As described above, computation involves three main steps:
The procedure involves three main steps:
Retrieve a set of time series and operations from (the Results table) of the database to a local Matlab file, HCTSA.mat (using SQL_Retrieve).
Compute the operations on the retrieved time series in Matlab and store the results locally (using TS_Compute).
Write the results back to the Results table of the database (using SQL_store).
It is usually the most efficient practice to retrieve a small number of time series at each iteration of the SQL_Retrieve–TS_Compute–SQL_store loop, and distribute this computation across multiple machines if possible. An example runscript is given in the code that accompanies this document, as sample_runscript_sql, which retrieves a single time series at a time, computes it, and then writes the results back to the database in a loop. This can be viewed as a template for runscripts that one may wish to use when performing time-series calculations across the database.
This workflow is well suited to distributed computing for large datasets, whereby each node can iterate over a small set of time series, with all the results being written back to a central location (the mySQL database).
By designating different sections of the database to cycle through, this procedure can also be used to (manually) distribute the computation across different machines. Retrieving a large section of the database at once can be problematic because it requires large disk reads and writes, uses a lot of memory, and if problems occur in the reading or writing to/from files, one may have to abandon a large number of existing computations.