Hi, On Fri, Jan 18, 2019 at 02:12:23PM +0000, Luis Carril wrote: > we noticed that in the presence of a schema with many partitions the > jitting overhead penalizes the total query execution time so much that the > planner should have decided not to jit at all. For example without jitting we > go a 8.3 s execution time and with jitting enabled 13.8 s. ... > Is this behavior expected? Is the cost function for jitting missing some > circumstances?
On Fri, Jan 18, 2019 at 08:42:54AM -0800, Andres Freund wrote: > The costing doesn't take the effect of overhead of repeated JITing in > each worker into account. I could give you a test patch that does, if > you want to play around with it? On Fri, Jan 18, 2019 at 06:02:43PM +0000, Luis Carril wrote: > yes please it would be much apreciated. I'm also interested to try that ; on re-enabling JIT in 11.2, I see that JITed queries seem to be universally slower than non-JIT. I found that was discussed here: https://www.postgresql.org/message-id/20180822161241.je6nghzjsktbb57b%40alap3.anarazel.de https://www.postgresql.org/message-id/20180624203633.uxirvmigzdhcyjsd%40alap3.anarazel.de Multiplying JIT cost by nworkers seems like an obvious thing to try, but I wondered whether it's really correct? Certainly repeated JITing takes N times more CPU time, but doesn't make the query slower...unless the CPU resources are starved and limiting ? Justin
