Re: shell and output redirection
- From: Mladen Gogala <mladen@xxxxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 2 Jul 2004 16:45:25 -0400
On 07/02/2004 04:18:26 PM, Tanel P?der wrote:
>
>
> Ok, but if program 1 will issue a write request to the pipe now, shall it
> post process 2 and not continue before process 2 has completed?
That is a part of pipe magic. Pipe blocks when it's full. The other program
will get to it, when it executes something like read(0,&buff, SIZE);
Pipes are "invisible" files allocated and mapped to the root file system.
(a version of WYSE Unix used to have a possibility to define the file
system used for pipes. That was extremely popular trick for benchmarking,
especially when PIPEFS was pointing to a solid state disk device. A company
that I worked for long, long time ago used to have a small solid state
device to which PIPEFS would be pointed and on which I would put redo log files.
Benchmarks against other manufacturers were great!). Unix (Linux) kernel will
usually allow pipes to grow few blocks before the pipe must be read. I should
go
and look for that part of Linux kernel, but I'm not up to the task tonight.
Hasta manana. I'll be back! (imagine me in a black leather jacket, with shades
on my nose).
>
> As I saw from your trace, shell uses pipe() to create the pipe file
> descriptors for passing on data between processes.
> What if I create a pipe manually using mknod and run my two processes
> manually, does the data streaming work exactly the same way that with
> shell-generated pipe?
It probably will have the same effect, if you do it right, but why would
you do it? Real programmers don't use tools provided by shell? It's called
"reinventing the wheel".
--
Mladen Gogala
Oracle DBA
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