Re: [sqlite] Difference between min and max time, especially for sys
2017-02-16 19:31 GMT+01:00 Jens Alfke : > > > On Feb 15, 2017, at 11:47 AM, Cecil Westerhof > wrote: > > > > But the difference between sys can be almost a factor twenty. What seems > very big to me. > > Yup. There is a huge speed difference between the kernel going to the > disk/SSD to read from a file, vs. the kernel reading the data out of its > buffer cache. That’s why the kernel has buffer caches :) > > (And those disk reads can be hugely variable. A hard disk can spend 10ms > or more seeking, and any medium has bandwidth limits, so other processes’ > I/O can greatly slow down your own. I’ve seen filesystem slowdowns of 20x > or more shortly after a user logs in when dozens of processes are launching > at once.) > Well user/sys is mostly around 10, so it does not have a to big influence on the measurements. ;-) -- Cecil Westerhof ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Difference between min and max time, especially for sys
> On Feb 15, 2017, at 11:47 AM, Cecil Westerhof wrote: > > But the difference between sys can be almost a factor twenty. What seems very > big to me. Yup. There is a huge speed difference between the kernel going to the disk/SSD to read from a file, vs. the kernel reading the data out of its buffer cache. That’s why the kernel has buffer caches :) (And those disk reads can be hugely variable. A hard disk can spend 10ms or more seeking, and any medium has bandwidth limits, so other processes’ I/O can greatly slow down your own. I’ve seen filesystem slowdowns of 20x or more shortly after a user logs in when dozens of processes are launching at once.) —Jens ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Difference between min and max time, especially for sys
On 15 Feb 2017, at 7:47pm, Cecil Westerhof wrote: > So the difference between minimum and maximum is about a factor two. What > seems reasonable to me. But the difference between sys can be almost a > factor twenty. What seems very big to me. Caching affects sys. Might be difference between time taken to fetch from disk and time taken when already in memory. Simon. ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
[sqlite] Difference between min and max time, especially for sys
I have several queries which I time with ‘.timer on’. I repeat the queries 350 times. I see a big difference between the minimum and maximum time needed to run the queries. Especially for sys. Like: Number of iterations 350 Timing OR version real: 120.86, min: 0.2710, max: 0.5540, max/min: 2.04 user: 110.10, min: 0.2360, max: 0.4760, max/min: 2.02 sys : 9.87, min: 0.0040, max: 0.0640, max/min: 16.00 Timing ABS version real: 108.96, min: 0.2730, max: 0.4850, max/min: 1.78 user: 97.67, min: 0.2320, max: 0.3720, max/min: 1.60 sys : 10.67, min: 0.0080, max: 0.0680, max/min: 8.50 Timing NOT BETWEEN version GOT A ZERO VALUE FOR SYS!!! real: 106.51, min: 0.2610, max: 0.4830, max/min: 1.85 user: 95.64, min: 0.2160, max: 0.4160, max/min: 1.93 sys : 10.14, min: 0.0040, max: 0.0760, max/min: 19.00 Timing NOT BETWEEN version 2 GOT A ZERO VALUE FOR SYS!!! real: 113.77, min: 0.2770, max: 0.5370, max/min: 1.94 user: 101.76, min: 0.2320, max: 0.4520, max/min: 1.95 sys : 11.24, min: 0.0040, max: 0.0680, max/min: 17.00 So the difference between minimum and maximum is about a factor two. What seems reasonable to me. But the difference between sys can be almost a factor twenty. What seems very big to me. Also it looks like SQLite suggests a precision it does not have. It shows four digits after the point, but it looks like that the smallest value greater as zero is 0.004. So why does SQLite not show three digits after the point? -- Cecil Westerhof ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
