elastic / ml-cpp

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[8.14][ML] Use custom Boost::JSON allocator (#2674) #2682

Closed edsavage closed 2 months ago

edsavage commented 2 months ago

The current code uses the monotonic resource allocator, for allocating memory to boost::json objects, which allocates memory in ever increasing chunks, which can lead to over allocation.

The other disadvantage of the monotonic resource allocator is that no deallocations are performed until the resource allocator is destroyed - hence the name monotonic as resource allocations can only increase during its lifetime.

These factors make the choice of the monotonic resource allocator unsuitable for its current use.

This PR introduces a very simplistic custom allocator that allocates and deallocates individual objects upon request using standard operator ::new and ::delete. This gives a much better experience as only as much memory is allocated at any point in time as absolutely needs to be, and gives a much more predictable memory profile

Backports #2674