=head1 NAME

udebug - Reports Ubik process status for a database server process

=head1 SYNOPSIS

=for html
<div class="synopsis">

B<udebug> S<<< B<-server> <I<server machine>> >>> S<<< [B<-port> <I<IP port>>] >>>
    [B<-long>] [B<-help>]

B<udebug> S<<< B<-s> <I<server machine>> >>> S<<< [B<-p> <I<IP port>>] >>> [B<-l>] [B<-h>]

=for html
</div>

=head1 DESCRIPTION

The B<udebug> command displays the status of the lightweight Ubik process
for the database server process identified by the B<-port> argument that
is running on the database server machine named by the B<-server>
argument. The output identifies the machines where peer database server
processes are running, which of them is the synchronization site (Ubik
coordinator), and the status of the connections between them.

=head1 OPTIONS

=over 4

=item B<-server> <I<server machine>>

Names the database server machine that is running the process for which to
display status information. Provide the machine's IP address in dotted
decimal format, its fully qualified host name (for example,
B<fs1.abc.com>), or the shortest abbreviated form of its host name that
distinguishes it from other machines. Successful use of an abbreviated
form depends on the availability of a name resolution service (such as the
Domain Name Service or a local host table) at the time the command is
issued.

=item B<-port> <I<IP port>>

Identifies the database server process for which to display status
information, either by its process name or port number. Provide one of the
following values.

=over 4

=item B<buserver> or 7021 for the Backup Server

=item B<kaserver> or 7004 for the Authentication Server

=item B<ptserver> or 7002 for the Protection Server

=item B<vlserver> or 7003 for the Volume Location Server

=back

=item B<-long>

Reports additional information about each peer of the machine named by the
B<-server> argument. The information appears by default if that machine
is the synchronization site.

=item B<-help>

Prints the online help for this command. All other valid options are
ignored.

=back

=head1 OUTPUT

Several of the messages in the output provide basic status information
about the Ubik process on the machine specified by the B<-server>
argument, and the remaining messages are useful mostly for debugging
purposes.

To check basic Ubik status, issue the command for each database server
machine in turn. In the output for each, one of the following messages
appears in the top third of the output.

   I am sync site . . . (<#_sites> servers)

   I am not sync site

For the synchronization site, the following message indicates that all
sites have the same version of the database, which implies that Ubik is
functioning correctly. See the following for a description of values other
than C<1f>.

   Recovery state 1f

For correct Ubik operation, the database server machine clocks must agree
on the time. The following messages, which are the second and third lines
in the output, report the current date and time according to the database
server machine's clock and the clock on the machine where the B<udebug>
command is issued.

   Host's <IP_addr> time is <dbserver_date/time>
   Local time is <local_date/time> (time differential <skew> secs)

The <skew> is the difference between the database server machine clock and
the local clock. Its absolute value is not vital for Ubik functioning, but
a difference of more than a few seconds between the I<skew> values for the
database server machines indicates that their clocks are not synchronized
and Ubik performance is possibly hampered.

Following is a description of all messages in the output. As noted, it is
useful mostly for debugging and most meaningful to someone who understands
Ubik's implementation.

The output begins with the following messages. The first message reports
the IP addresses that are configured with the operating system on the
machine specified by the B<-server> argument. As previously noted, the
second and third messages report the current date and time according to
the clocks on the database server machine and the machine where the
B<udebug> command is issued, respectively. All subsequent timestamps in
the output are expressed in terms of the local clock rather than the
database server machine clock.

   Host's addresses are: <list_of_IP_addrs>
   Host's <IP_addr> time is <dbserver_date/time>
   Local time is <local_date/time> (time differential <skew> secs)

If the <skew> is more than about 10 seconds, the following message
appears. As noted, it does not necessarily indicate Ubik malfunction: it
denotes clock skew between the database server machine and the local
machine, rather than among the database server machines.

   ****clock may be bad

If the udebug command is issued during the coordinator election process
and voting has not yet begun, the following message appears next.

   Last yes vote not cast yet

Otherwise, the output continues with the following messages.

   Last yes vote for <sync_IP_addr> was <last_vote> secs ago (sync site);
   Last vote started <vote_start> secs ago (at <date/time>)
   Local db version is <db_version>

The first indicates which peer this Ubik process last voted for as
coordinator (it can vote for itself) and how long ago it sent the vote.
The second message indicates how long ago the Ubik coordinator requested
confirming votes from the secondary sites. Usually, the <last_vote> and
<vote_start> values are the same; a difference between them can indicate
clock skew or a slow network connection between the two database server
machines. A small difference is not harmful. The third message reports the
current version number <db_version> of the database maintained by this
Ubik process. It has two fields separated by a period. The field before
the period is based on a timestamp that reflects when the database first
changed after the most recent coordinator election, and the field after
the period indicates the number of changes since the election.

The output continues with messages that differ depending on whether the
Ubik process is the coordinator or not.

=over 4

=item *

If there is only one database server machine, it is always the coordinator
(synchronization site), as indicated by the following message.

   I am sync site forever (1 server)

=item *

If there are multiple database sites, and the B<-server> argument names
the coordinator (synchronization site), the output continues with the
following two messages.

   I am sync site until <expiration> secs from now (at <date/time>)
       (<#_sites> servers)
   Recovery state <flags>

The first message (which is reported on one line) reports how much longer
the site remains coordinator even if the next attempt to maintain quorum
fails, and how many sites are participating in the quorum. The I<flags>
field in the second message is a hexadecimal number that indicates the
current state of the quorum. A value of C<1f> indicates complete database
synchronization, whereas a value of C<f> means that the coordinator has
the correct database but cannot contact all secondary sites to determine
if they also have it. Lesser values are acceptable if the B<udebug>
command is issued during coordinator election, but they denote a problem
if they persist. The individual flags have the following meanings:

=over 4

=item 0x1

This machine is the coordinator.

=item 0x2

The coordinator has determined which site has the database with the
highest version number.

=item 0x4

The coordinator has a copy of the database with the highest version
number.

=item 0x8

The database's version number has been updated correctly.

=item 0x10

All sites have the database with the highest version number.

=back

If the udebug command is issued while the coordinator is writing a change
into the database, the following additional message appears.

   I am currently managing write transaction I<identifier>

=item *

If the B<-server> argument names a secondary site, the output continues
with the following messages.

   I am not sync site
   Lowest host <lowest_IP_addr> was set <low_time> secs ago
   Sync host <sync_IP_addr> was set <sync_time> secs ago

The <lowest_IP_addr> is the lowest IP address of any peer from which the
Ubik process has received a message recently, whereas the <sync_IP_addr>
is the IP address of the current coordinator. If they differ, the machine
with the lowest IP address is not currently the coordinator. The Ubik
process continues voting for the current coordinator as long as they
remain in contact, which provides for maximum stability. However, in the
event of another coordinator election, this Ubik process votes for the
<lowest_IP_addr> site instead (assuming they are in contact), because it
has a bias to vote in elections for the site with the lowest IP address.

=back

For both the synchronization and secondary sites, the output continues
with the following messages. The first message reports the version number
of the database at the synchronization site, which needs to match the
<db_version> reported by the preceding C<Local db version> message. The
second message indicates how many VLDB records are currently locked for
any operation or for writing in particular. The values are nonzero if the
B<udebug> command is issued while an operation is in progress.

   Sync site's db version is <db_version>
   <locked> locked pages, <writes> of them for write

The following messages appear next only if there are any read or write
locks on database records:

   There are read locks held
   There are write locks held

Similarly, one or more of the following messages appear next only if there
are any read or write transactions in progress when the B<udebug> command
is issued:

   There is an active write transaction
   There is at least one active read transaction
   Transaction tid is <tid>

If the machine named by the B<-server> argument is the coordinator, the
next message reports when the current coordinator last updated the
database.

    Last time a new db version was labelled was:
            <last_restart> secs ago (at <date/time>)

If the machine named by the B<-server> argument is the coordinator, the
output concludes with an entry for each secondary site that is
participating in the quorum, in the following format.

   Server (<IP_address>): (db <db_version>)
   last vote rcvd <last_vote> secs ago (at <date/time>),
   last beacon sent <last_beacon> secs ago (at <date/time>),
       last vote was { yes | no }
   dbcurrent={ 0 | 1 }, up={ 0 | 1 } beaconSince={ 0 | 1 }

The first line reports the site's IP address and the version number of the
database it is maintaining. The <last_vote> field reports how long ago the
coordinator received a vote message from the Ubik process at the site, and
the <last_beacon> field how long ago the coordinator last requested a vote
message. If the B<udebug> command is issued during the coordinator
election process and voting has not yet begun, the following messages
appear instead.

   Last vote never rcvd
   Last beacon never sent

On the final line of each entry, the fields have the following meaning:

=over 4

=item *

C<dbcurrent> is C<1> if the site has the database with the highest version
number, C<0> if it does not.

=item *

C<up> is C<1> if the Ubik process at the site is functioning correctly,
C<0> if it is not.

=item *

C<beaconSince> is C<1> if the site has responded to the coordinator's last
request for votes, C<0> if it has not.

=back

Including the B<-long> flag produces peer entries even when the
B<-server> argument names a secondary site, but in that case only the
I<IP_address> field is guaranteed to be accurate. For example, the value
in the <db_version> field is usually C<0.0>, because secondary sites do
not poll their peers for this information.  The values in the I<last_vote>
and I<last_beacon> fields indicate when this site last received or
requested a vote as coordinator; they generally indicate the time of the
last coordinator election.

=head1 EXAMPLES

This example checks the status of the Ubik process for the Volume Location
Server on the machine C<afs1>, which is the synchronization site.

   % udebug afs1 vlserver
   Host's addresses are: 192.12.107.33
   Host's 192.12.107.33 time is Wed Oct 27 09:49:50 1999
   Local time is Wed Oct 27 09:49:52 1999 (time differential 2 secs)
   Last yes vote for 192.12.107.33 was 1 secs ago (sync site);
   Last vote started 1 secs ago (at Wed Oct 27 09:49:51 1999)
   Local db version is 940902602.674
   I am sync site until 58 secs from now (at Wed Oct 27 09:50:50 1999) (3 servers)
   Recovery state 1f
   Sync site's db version is 940902602.674
   0 locked pages, 0 of them for write
   Last time a new db version was labelled was:
            129588 secs ago (at Mon Oct 25 21:50:04 1999)

   Server( 192.12.107.35 ): (db 940902602.674)
       last vote rcvd 2 secs ago (at Wed Oct 27 09:49:50 1999),
       last beacon sent 1 secs ago (at Wed Oct 27 09:49:51 1999), last vote was yes
       dbcurrent=1, up=1 beaconSince=1

   Server( 192.12.107.34 ): (db 940902602.674)
       last vote rcvd 2 secs ago (at Wed Oct 27 09:49:50 1999),
       last beacon sent 1 secs ago (at Wed Oct 27 09:49:51 1999), last vote was yes
       dbcurrent=1, up=1 beaconSince=1

This example checks the status of the Authentication Server on the machine
with IP address 192.12.107.34, which is a secondary site. The local clock
is about 4 minutes behind the database server machine's clock.

   % udebug 192.12.107.34 7004
   Host's addresses are: 192.12.107.34
   Host's 192.12.107.34 time is Wed Oct 27 09:54:15 1999
   Local time is Wed Oct 27 09:50:08 1999 (time differential -247 secs)
   ****clock may be bad
   Last yes vote for 192.12.107.33 was 6 secs ago (sync site);
   Last vote started 6 secs ago (at Wed Oct 27 09:50:02 1999)
   Local db version is 940906574.25
   I am not sync site
   Lowest host 192.12.107.33 was set 6 secs ago
   Sync host 192.12.107.33 was set 6 secs ago
   Sync site's db version is 940906574.25
   0 locked pages, 0 of them for write

=head1 PRIVILEGE REQUIRED

None

=head1 SEE ALSO

L<buserver(8)>,
L<kaserver(8)>,
L<ptserver(8)>,
L<vlserver(8)>

=head1 COPYRIGHT

IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.

This documentation is covered by the IBM Public License Version 1.0.  It was
converted from HTML to POD by software written by Chas Williams and Russ
Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.
