[fpc-pascal] File Enumeration speed

[SteveG]

On 28/07/12 19:58, Michael Van Canneyt wrote:
>
>
> On Sat, 28 Jul 2012, SteveG wrote:
>
>> I am enumerating thru large numbers of files on my disk, and find I 
>> cant come close with findfirst / findnext to matching the speed of 
>> cmd line apps available in linux :eg ls / du
>
> A regular ls only does a getdents() call.
>
> FindFirst/FindNext does a getdents, but then additionally, per file in 
> the result, a stat() call.
>
>> I have a fairly tight file search function, and dont see how to gain 
>> more speed
>>
>> Would anybody know what the limiting factors would be ?
>
> The number of calls to stat() to get extended file information.
>
> I suspect that if  you do a ls -l, it will be as slow as 
> findfirst/findnext, because it does then 3 calls per file:
>
> from strace ls -l /etc I get:
>
> lstat("/etc/odbc.ini", {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
> lgetxattr("/etc/odbc.ini", "security.selinux", 0x14de920, 255) = -1 
> ENODATA (No data available)
> getxattr("/etc/odbc.ini", "system.posix_acl_access", 0x0, 0) = -1 
> EOPNOTSUPP (Operation not supported)
>
> If you want speedier operation, and have enough file information with 
> the name, you can simply do a getdents().
>
>> does the operating system keep an index somewhere ?
>
> Normally not (at least other than the regular disc cache).
>
>
Thanks Michael - I will do some study (ie find out what getdents() does)