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While JIT can speed up large analytical queries, it can also cause serious performance issues on otherwise very fast queries. Compiling and optimizing the expressions may be so expensive, it completely outweighs the JIT benefits for shorter queries. Ideally, we'd address this in the cost model, but the part deciding whether to enable JIT for a query is rather simple, partially because we don't have any reliable estimates of how expensive the LLVM compilation and optimization is. Sometimes seemingly unrelated changes (for example a couple additional INSERTs into a table) increase the cost just enough to enable JIT, resulting in a performance cliff. Because of these risks, most large-scale deployments already disable JIT by default. Notably, this includes all hyperscalers. This commit changes our default to align with that established practice. If we improve the JIT (be it better costing or cheaper execution), we can consider enabling it by default again. Author: Jelte Fennema-Nio <postgres@jeltef.nl> Discussion: https://postgr.es/m/DG1VZJEX1AQH.2EH4OKGRUDB71@jeltef.nl |
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