![]() ![]() however, if DBLWR feature is providing the necessary security for user's data, it's also increasing page write latency by x2 (in the best case) or more, and also, as the result, reducing by x2 life of any flash storage by sending twice higher IO write traffic for the same data.each page we first write to some "reserved place", and once the write is confirmed, we then write this page to its own place in its datafile, so if there was any crash in the middle, we can re-apply page write from DBLWR (or discard DBLWR record if the crash happened on DBLWR write). so, DBLWR is here to protect InnoDB pages writes from partially written data.in fact historically (and still right now) Linux kernel/ FS layer cannot guarantee atomic IO writes.however, since last few years we seriously addressed the problems we have in InnoDB Double-Write (DBLWR) feature.there were many tentatives to bring XFS on front, but, again, historically, there were always some issues as soon as workload became IO-bound.historically with MySQL we always observed better performance and more stable processing on EXT4.NOTE : this will also clarify why the new Double Write did not appear in MySQL 8.0 in 2018, as it was planned, but only recently ( ) First of all, some background history And I'm constantly asked "why, Dimitri, you're suggesting now to use XFS, while in the past you always suggested EXT4 ?" - hope the following article will clarify you the "why" and maybe motivate you to do your own evaluations to see how well the things are working for you on your own systems under your own workloads. But time is going, and the problems are remaining. This post was remaining in stand-by for a long time, specially that I was expecting that observed issues will be fixed soon. ![]()
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