How can it crunch through 1GB in 1s? Even just reading the data would take longer on any system I know.
In this case isn't the "already in RAM" test a more accurate reflection of performance anyway, as we are talking about the performance of grep and not the IO subsystem?
There are many cases where grep's performance won't be bottlenecked by IO, or at least not impacted directly by a bottleneck there. Anywhere when the input is coming from another program, essentially, and even if that task is IO bound it might be sending output to grep much faster than it is consuming input (perhaps gunzip <file | grep searchtext).
And in the case of searching a log file interactively, it is common that you won't just run grep of the file just once in a short space of time, instead doing it a couple of times as you refine your search, so for most of the runs it will be in cache (assuming the file is not to large).
Nearly ever SSD listed achieves well over 1GB/s in an actual benchmark, not just on a spec sheet. And these are just boring old off the shelf consumer drives. Nothing crazy.
So yeah maybe not over 400MB/s, but all of them are over 200MB/s. Sequential speeds really spiked as densities kept increasing.
Note that you're not going to get this with SATA SSDs, you need NVMe, it's a 5x difference in throughput and IOPS.
That's a very common use-case with grep. Either grepping a file you recently wrote, or running grep multiple times as you refine the regex, at which point the files will be in the FS cache.
> #1 trick: GNU grep is fast because it AVOIDS LOOKING AT EVERY INPUT BYTE.
TFA is incredibly short, and will explain it much better than I can.
This would not help, since the backing storage doesn't provide support for this kind of resolution. It would end up reading in the entire file anyways, unless your input string is on the order of an actual block.
As the other reply mentioned though, it's just that MacBook SSDs are that fast.
Somewhat confusing since it has to look at every byte to find the newlines. They are using a pretty specific definition of "look".
> Moreover, GNU grep AVOIDS BREAKING THE INPUT INTO LINES. Looking for newlines would slow grep down by a factor of several times, because to find the newlines it would have to look at every byte!
I assume the Boyer Moore preprocessor reads a lot of bytes also.
Not disputing it's more efficient, but there's no magic. It avoids reading some bytes when and if it can.
It can whenever you don't ask for line numbers, can't it?
> It probably looks for newlines after a match is found
Probably, yeah. Counting number of newlines in a range, without caring just where they fall, can probably be pretty darned fast with vector instructions. Idk if that's worth the additional pass, though.
Another way of looking at is just considering the ^ another character (plus one-off special handling for start of file).
It's also possible that the file is cached in memory (I ran grep a few times through the file before I carried out the specific measurements).
If we assume something like 100 MB/s sustained for spinning disks, that's a lot of disks to get to 2.41 GB/s even ignoring overheads.
This test was hitting the OS disk cache.
Samsung's PM1725b (https://www.samsung.com/semiconductor/ssd/enterprise-ssd/MZP...) has a Seq. Read of 6300 MB/s and Seq. Write of 3300 MB/s.