Re: When is usexhdr useful in leafnode 2?

On Mon, 30 Jun 2014 13:47:16 +0100 Adam Funk <a24061-yXNeHEYmD9/[email protected]> wrote:

>The man page for leafnode 2 says:
>
>  usexhdr = 1
>    fetchnews will usually use XOVER to retrieve header information
>    from the remote server.  Under special circumstances, it may be
>    faster to have it use XHDR instead.  This line will try to enforce
>    XHDR, but fetchnews will still fall back to XOVER if you also want
>    to use filters in a group or if you work with "delaybody" set
>    (because in these cases it will always be faster to use XOVER).
>
>What are the mysterious "special circumstances"?
>
>I've just noticed the "config: usexhdr does not work together with
>filtering or delaybody mode" warning in my logs; my config file has
>"usexhdr = 1" under nntp.aioe.org, but not in any of the other
>upstream server configs, & I can't recall when or why I put it there!
>
>Thanks,
>Adam

One returns all headers and body for the specified MID(s), the other can return
specified fields only.  (We're supposed not to use the X in the command names
now).  

One circumstance in which HDR might be quicker, is if you need to retrieve only
one header and your connection to the server is very slow.  I think HDR may
make more work for the upstream server.

The HDR command can be used eg to extract the References header from a given
article and from that issue the OVER commend for each of the MIDs revealed;
useful if you want to reconstruct a thread.  (Slrn seems to work that way to
reconstruct a thread - which it can do when connected to Leafnode 2 but not
with Leafnode 1 which doesn't support HDR).

,----<http://tools.ietf.org/html/rfc3977>
| [...]
|
| 8.3.2.  Description
|
|    The OVER command returns the contents of all the fields in the
|    database for an article specified by message-id, or from a specified
|    article or range of articles in the currently selected newsgroup.
|
| [...]
|
| 8.5.2.  Description
|
|    The HDR command provides access to specific fields from an article
|    specified by message-id, or from a specified article or range of
|    articles in the currently selected newsgroup.  It MAY take the
|    information directly from the articles or from the overview database.
|    In the case of headers, an implementation MAY restrict the use of
|    this command to a specific list of headers or MAY allow it to be used
|    with any header; it may behave differently when it is used with a
|    message-id argument and when it is used with a range or no argument.
|
| [...]
`----

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