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Frequently Asked Questions

There is a related page of Common Installation Problems.

How to recover from a corrupted ODB

Stop your front-ends

mlogger, mhttpd, etc.

Remove the shared memory associated to your experiment

Find the shared memory segment by doing

ls -l /dev/shm

then use the rm command to delete the segments that are contain your experiment name.

If you have the MIDAS_EXPT_NAME environment variable defined, you can just do:

rm /dev/shm/${MIDAS_EXPT_NAME}_*SHM

Move or delete the old .SHM files

These will be in the location given by Exptab, e.g. ~/online

# Either move some of the files...
cd online
mv .ODB.SHM .ODB.SHM.BAD
mv .SYSMSG.SHM .SYSMSG.SHM.BAD
mv .MSG.SHM .MSG.SHM.BAD

# .. or just delete all of them
cd online
rm .*SHM*

Recreate ODB with larger size and reload the last saved ODB dump you have

See save and reload the ODB) for more about ODB dumps.

These dumps are typically called something like 'online/history/*.xml'.

To find the correct file:

• The dumps are .xml, .odb or .json files.
• Depending on your mlogger ODB settings ('/Logger/ODB Dump', '/Logger/ODB Dump File', and '/Logger/ODB Last Dump File'), you may have files named based on run numbers or just 'last.json' etc. If using run numbers, you almost certainly want to load the most recent one.
• The files are stored in the same location as the midas history data (based on '/Logger/History dir' or '/Logger/Data dir).

Once you have found the correct file, run a command like:

odbedit -s 100000000 -c "load online/history/run001234.xml"'
or
odbedit -s 100000000 -c "load online/history/last.json"'
etc.

The -s argument indicates to recreate an empty ODB with a new size (in bytes). The -c argument specifies the file to use to populate the new ODB.

Your ODB should now be fixed

See also odbinit.

How to get odbedit to show run state

Question: I've seen the ODB prompt displaying the run state, how do you do that?

Answer: Modify the /System/prompt field. The "S" is the trick.

 Fri> odb -e bnmr1 -h isdaq01
 [host:expt:Stopped]/cd /System/
 [host:expt:Stopped]/System>ls
 Clients
 Client Notify                   0
 Prompt                          [%h:%e:%S]%p
 Tmp
 [host:expt:Stopped]/System
 [host:expt:Stopped]/Systemset prompt [%h:%e:%S]%p>
 [host:expt:Stopped]/System>ls
 Clients
 Client Notify                   0
 Prompt                          [%h:%e:%S]%p>
 Tmp
 [host:expt:Stopped]/System>set Prompt [%h:%e:%s]%p>
 [host:expt:S]/System>set Prompt [%h:%e:%S]%p>
 [host:expt:Stopped]/System>     

See also /System ODB tree#Prompt.

Increasing Number of Hot-links

MIDAS, by default, allows you to have a maximum of 256 individual hot-links to be registered. If you find that you need more hot-links than that, follow the procedure below:

1. Use odbedit to save current ODB

   odbedit
   save current_odb.odb 
   

2. Stop all the running MIDAS processes, including mlogger and mserver using the web interface. Then stop mhttpd as well. To stop mhttpd just do

   killall mhttpd
   

3. Remove your old ODB (we will recreate it after modifying MIDAS, using the backup you just made).

   mv .ODB.SHM .ODB.SHM.20161104
   rm /dev/shm/<expname>_ODB_SHM
   

   where <expname> is the name of your experiment.

4. Make the following modifications to midas. In this particular case I have increased the max number of open records from 256 to 1024. You would need to change the constants if you want to change to other values

   diff --git a/include/midas.h b/include/midas.h
   index 02b30dd..33be7be 100644
   --- a/include/midas.h
   +++ b/include/midas.h
   @@ -254,7 +254,7 @@ typedef std::vector<std::string> STRING_LIST;
   -#define MAX_OPEN_RECORDS       256           /**< number of open DB records   */
   +#define MAX_OPEN_RECORDS       1024           /**< number of open DB records   */
   diff --git a/src/odb.c b/src/odb.c
   index 47ace8f..ac1bef3 100755
   --- a/src/odb.c
   +++ b/src/odb.c
   @@ -699,8 +699,8 @@ static void db_validate_sizes()
   -   assert(sizeof(DATABASE_CLIENT) == 2112);
   -   assert(sizeof(DATABASE_HEADER) == 135232);
   +   assert(sizeof(DATABASE_CLIENT) == 8256);
   +   assert(sizeof(DATABASE_HEADER) == 528448);
   

   The calculation is as follows (in case you want a different number of open records): DATABASE_CLIENT = 64 + 8*MAX_OPEN_ERCORDS = 64 + 8*1024 = 8256 DATABASE_HEADER = 64 + 64*DATABASE_CLIENT = 64 + 64*8256 = 528448

5. Rebuild MIDAS

   cd $MIDASSYS
   make clean; make
   

6. Create new ODB

   odbedit -s 1000000
   

   Note, you should change the size of the ODB to whatever you need.

7. reload your original ODB

   [local:exp:Stopped] load  current_odb.odb
   

8. Rebuild all your frontend programs (and other user-specific programs) against new MIDAS; they should then work and you should be able to produce more open records.