Increase local breaker reserve memory #133770
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elasticsearchmachine
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martijnvg
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JeremyDahlgren
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Aug 29, 2025
Currently, we use a local breaker that over-reserves memory for each driver to reduce frequent calls to the global circuit breaker, which can be expensive. After reviewing some profiles, the maximum reserved amount appears too small and does not significantly reduce calls to the global breaker. The reserved amount should cover at least several pages of data (~256KB by default). This change proposes increasing the maximum reserved to two pages (512KB). One downside is that we may hit the circuit breaker earlier under extremely tight memory conditions, but the impact should be minimal. For example, on a node with 8 CPUs, the total reserved could be 12 * 0.5 = 6MB. In cases with many long-running queries that frequently wake and sleep, the extra over-reserved memory may be more noticeable. However, even with 100 drivers, the total maximum would be only 50MB.
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Currently, we use a local breaker that over-reserves memory for each driver to reduce frequent calls to the global circuit breaker, which can be expensive. After reviewing some profiles, the maximum reserved amount appears too small and does not significantly reduce calls to the global breaker.
The reserved amount should cover at least several pages of data (~256KB by default). This change proposes increasing the maximum reserved to two pages (512KB). One downside is that we may hit the circuit breaker earlier under extremely tight memory conditions, but the impact should be minimal. For example, on a node with 8 CPUs, the total reserved could be 12 * 0.5 = 6MB. In cases with many long-running queries that frequently wake and sleep, the extra over-reserved memory may be more noticeable. However, even with 100 drivers, the total maximum would be only 50MB.