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Displaying posts with tag: MySQL SSD (reset)
Why Consumer SSD Reviews are Useless for Database Performance Use Case

If you’re reading consumer SSD reviews and using them to estimate SSD performance under database workloads, you’d better stop. Databases are not your typical consumer applications and they do not use IO in the same way.

Let’s look, for example, at this excellent AnandTech review of Samsung 960 Pro –  a consumer NVMe device that I happen to have in my test lab.

The summary table is actually great, showing the performance both at Queue Depth 1 (single threaded) as well as Queue Depth 32 – a pretty heavy concurrent load.

Even at QD1 we see 50K (4K) writes per second, which should be enough for pretty serious database workloads.

In reality, though, you might be in for some disappointing surprises. While “normal” buffered IO is indeed quite fast, this drive really hates fsync() calls, with a single thread …

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Discussing the innodb_log_block_size variable

Not a ground-breaking post here, but if you are interested in knowing more about the innodb_log_block_size variable, or if you use SSD cards and/or large InnoDB log files on ext4, then this is for you.

I’d read about it before briefly before, but didn’t give it too much thought until I ran across the following entry in an error log the other day:

InnoDB: Warning: innodb_log_block_size has been changed
from default value 512. (###EXPERIMENTAL### operation)

This got me wanting to know more.

Basically, this variable changes the size of transaction log records. Generally, the default of 512 is a good value. However, it has been found that setting it to 4096 has been beneficial when using SSD cards. (Note that while it is possible to set this to a value other than 512 or 4096, those are currently the only 2 values that make sense to use.)

Also, it has been found that 4096 is the best setting if you run …

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