Attached is an extremely crude prototype patch for making VACUUM delay by a configurable amount between pages, in hopes of throttling its disk bandwidth consumption. By default, there is no delay (so no change in behavior). In some quick testing, setting vacuum_page_delay to 10 (milliseconds) seemed to greatly reduce a background VACUUM's impact on pgbench timing on an underpowered machine. Of course, it also makes VACUUM a lot slower, but that's probably not a serious concern for background VACUUMs.
[SNIP]
The patch is against CVS tip, but should apply cleanly to any recent 7.4 beta. You could likely adapt it to 7.3 without much effort.
Will we have this on 7.4 ? I tried it and improve a lot the responsiness of my queries just putting the delay equal to 10 ms.
Regards Gaetano Mendola
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