Detecting chains of functions that violate a constraint

A method of a distributed system comprising a plurality of computing nodes and a plurality of server processes executed by the plurality of computing nodes, the method comprising:

• invoking user-defined functions (UDFs) for execution in respective server processes of the plurality of server processes, wherein a first UDF in a first server process invokes a second UDF for execution in a second server process, wherein each respective server process of the plurality of server processes comprises a virtual environment that defines an isolated computing environment for execution of a respective UDF, and wherein a UDF comprises a function developed by an entity and is not part of a database programming language;
• as the UDFs are invoked and executed by the respective server processes, adding key-value pairs to entries of a tracking structure in a cache, wherein each respective key-value pair of the key-value pairs comprises a key that identifies a program instance a corresponding UDF is associated with, and a value that identifies the corresponding UDF, wherein the adding comprises a first server process adding a first key-value pair to a first entry of the tracking structure in response to invocation of a first UDF, and a second server process adding a second key-value pair to a second entry of the tracking structure in response to invocation of a second UDF;
• determining, by a monitor process based on the key-value pairs in the tracking structure, whether a chain of UDFs violates a constraint, wherein the monitor process comprises machine-readable instructions to monitor the tracking structure;
• and
• in response to determining that the chain of UDFs violates the constraint, blocking, by a server process, invocation of a further UDF.