ESQL: Limit memory usage of fold (#118602)
#120100
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`fold` can be surprisingly heavy! The maximally efficient/paranoid thing would be to fold each expression one time, in the constant folding rule, and then store the result as a `Literal`. But this PR doesn't do that because it's a big change. Instead, it creates the infrastructure for tracking memory usage for folding as plugs it into as many places as possible. That's not perfect, but it's better. This infrastructure limit the allocations of fold similar to the `CircuitBreaker` infrastructure we use for values, but it's different in a critical way: you don't manually free any of the values. This is important because the plan itself isn't `Releasable`, which is required when using a real CircuitBreaker. We could have tried to make the plan releasable, but that'd be a huge change. Right now there's a single limit of 5% of heap per query. We create the limit at the start of query planning and use it throughout planning. There are about 40 places that don't yet use it. We should get them plugged in as quick as we can manage. After that, we should look to the maximally efficient/paranoid thing that I mentioned about waiting for constant folding. That's an even bigger change, one I'm not equipped to make on my own.
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Jan 15, 2025
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foldcan be surprisingly heavy! The maximally efficient/paranoid thing would be to fold each expression one time, in the constant folding rule, and then store the result as aLiteral. But this PR doesn't do that because it's a big change. Instead, it creates the infrastructure for tracking memory usage for folding as plugs it into as many places as possible. That's not perfect, but it's better.This infrastructure limit the allocations of fold similar to the
CircuitBreakerinfrastructure we use for values, but it's different in a critical way: you don't manually free any of the values. This is important because the plan itself isn'tReleasable, which is required when using a real CircuitBreaker. We could have tried to make the plan releasable, but that'd be a huge change.Right now there's a single limit of 5% of heap per query. We create the limit at the start of query planning and use it throughout planning.
There are about 40 places that don't yet use it. We should get them plugged in as quick as we can manage. After that, we should look to the maximally efficient/paranoid thing that I mentioned about waiting for constant folding. That's an even bigger change, one I'm not equipped to make on my own.