Performance Tuning
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Reading news on a server witch does not have a NOV database
A NOV (News overview) database holds information about each available article, for example the article's subject, the "From" header etc. When a user selects a newsgroup, Alexandra fetches these information via the non-standard NNTP command "XOVER". Older newsreaders had to get the full header of each article to show the user the list of accessible articles in advance.

If your NNTP server does not understand the XOVER command, Alexandra uses the non-standard XHDR command to extract the same information. This command is supported by all nntp servers I know of. The XDHR command returns only one header, so Alexandra issues at most 5 XHDR commands to get all required information. Because the server has to parse each article 5 times, article prefetching may be slow. You can speed up prefetching by reducing the number of issued commands. If you do that, Alexandra will disable some functions. (See below)

Some NNTP servers offer the XOVER command even if they don't have a NOV database. Then each article is only accessed once.

Reading news on a server witch does not have a NOV database
A NOV (News overview) database holds information about each available article, for example the article's subject, the "From" header etc. When a user selects a newsgroup, Alexandra fetches these information via the non-standard NNTP command "XOVER". Older newsreaders had to get the full header of each article to show the user the list of accessible articles in advance.

If your NNTP server does not understand the XOVER command, Alexandra uses the non-standard XHDR command to extract the same information. This command is supported by all nntp servers I know of. The XDHR command returns only one header, so Alexandra issues at most 5 XHDR commands to get all required information. Because the server has to parse each article 5 times, article prefetching may be slow. You can speed up prefetching by reducing the number of issued commands. If you do that, Alexandra will disable some functions. (See below)
Some NNTP servers offer the XOVER command even if they don't have a NOV database. Then each article is only accessed once.

Reading news via a slow connection
If you read your news via a slow connection like a 14.4 modem, you may want to enable the SLOW LINK feature.  If its enabled, Alexandra.app does not issue the "LIST" command. This command returns the names of all currently valid newsgroups. Over a slow connection, this may take some time. Checking the "slow link" button in the nntp server panel suppresses the "LIST" command. If this feature is enabled, expired newsgroups are not removed from your newsgroup list and you can't see the number of unread articles of any unsubscribed newsgroup.

Note that if you open a server the first time, the LIST command is issued even if the slow link feature is enabled!!!

You also may want to disable the use of the NOV database to speed up the article prefetching time. If your connection is real slow, you can disable NOV and prefetch no optional header.

Relevant application defaults
NOTE: None of the defaults can be set in the preferences panel. If you switch off the prefetching of header "X", you can't search in the article list for the content of header "X".
Lets say that your server name is foobar. Close any NNTP connection to foobar.

In Terminal.app write:
dwrite Alexandra "DoNotUseNov foobar" YES
to let Alexandra use the "XHDR" command instead of the "XOVER" command. All other defaults have no effect if this default is not set to "YES".

dwrite Alexandra "DoNotPrefetchFrom foobar" YES
to let Alexandra not prefetch the "From" headers of each article. If this is enabled, you can't see the authors name of each article in advance and you can't sort the article list by the authors real name. Author killing is disabled.

dwrite Alexandra "DoNotPrefetchMsgid foobar" YES
to let Alexandra not prefetch the message id of each article.

dwrite Alexandra "DoNotPrefetchRefs foobar" YES
to let Alexandra not prefetch the "References" headers.

dwrite Alexandra "DoNotPrefetchDate foobar" YES
to let Alexandra not prefetch the "Date" headers. You can't sort the article list by date, if this is enabled.

dwrite Alexandra "DoNotPrefetchLines foobar" YES
to let Alexandra not prefetch the "Lines" header. You can't see the articles size in advance, if this is enabled.