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Thread: Clarification needed for comment in storage/file/fd.c

Clarification needed for comment in storage/file/fd.c

From
samuel cherukutty
Date:
Hi, 
     I came across this comment in storage/file/fd.c while I was trying to write an FDW.

" AllocateFile, AllocateDir, OpenPipeStream and OpenTransientFile are
wrappers around fopen(3), opendir(3), popen(3) and open(2), respectively.
They behave like the corresponding native functions, except that the handle
is registered with the current subtransaction, and will be automatically
closed at abort. These are intended mainly for short operations like
reading a configuration file; there is a limit on the number of files that
can be opened using these functions at any one time. "

It states that it behaves as native functions with the handle registered to the current subtransaction. 
If it is so, why is it intended for short operations?
Will it work if I open a file at the start of the transaction and close it at the end of the transaction?
What are the side effects/limitations of these functions?

Regards,
Samuel CC




Re: Clarification needed for comment in storage/file/fd.c

From
Michael Paquier
Date:
On Thu, Mar 15, 2018 at 11:22:31AM +0000, samuel cherukutty wrote:
> It states that it behaves as native functions with the handle
> registered to the current subtransaction.
> If it is so, why is it intended for short operations?
> Will it work if I open a file at the start of the transaction and
> close it at the end of the transaction?
> What are the side effects/limitations of these functions?

The maximum number of file descriptors can be tuned using
max_files_per_process, however the more concurrent operations you do,
the higher the risk to run out of them.  Hence limiting them for
short-time operations it preferred to keep things stable.  You actually
never need to hold them that long anyway, and you may want to rethink
what you are doing as well.
--
Michael
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