From: "Andres Freund" <>
On 2014-02-18 00:43:54 +0900, MauMau wrote:
I'm worried about the big increase in max latency. Do you know the cause? More frequent checkpoints caused by increased WAL volume thanks to enhanced

I don't see much evidence of increased latency there? You can't really
compare the latency when the throughput is significantly different.

For example, please see the max latencies of test set 2 (PG 9.3) and test set 4 (xlog scaling with padding). They are 207.359 and 1219.422 respectively. The throughput is of course greatly improved, but I think the response time should not be sacrificed as much as possible. There are some users who are sensitive to max latency, such as stock exchange and online games.

Although I'm not sure this is related to what I'm asking, the following code
fragment in WALInsertSlotAcquireOne() catched my eyes.  Shouldn't the if
condition be "slotno == -1" instead of "!="? I thought this part wants to make inserters to use another slot on the next insertion, when they fail to acquire the slot immediately. Inserters pass slotno == -1. I'm sorry if I
misunderstood the code.

I think you're right.

Thanks for your confirmation. I'd be glad if the fix could bring any positive impact on max latency.


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