The Model 204 DBMS can run in a number of modes, BATCH204 and Online being the primary two. In both cases Model 204 appears as a single address space on the operator console under z/OS and VSE, or as a virtual machine under VM.
In the early history of Model 204, this distinction resulted in the somewhat odd use of the word
Online as a noun. Specifically, as a shorthand for referring to the address space, region, or virtual machine running Model 204 in Online mode, people would just refer to an "Online". For example, someone might say, "The production Online is running a bit slow, today," or "Can you log into the test Online and look at something for me?" This shorthand is convenient, and it is ubiquitous in the Model 204 community, so it is used heavily in much of the Model 204 documentation.
In Batch mode, Model 204 is defined with no input/output devices (aka IODEV threads, or just IODEVs), and runs as a single batch user, executing all the commands and programs in the CCAIN DD, until the command stream is exhausted, after which the job stops.
In Online mode, Model 204 is defined as a single "batch" user (aka "User 0") with a number of online users. Here too, the job runs, executing all commands in CCAIN until the job completes. The purpose of an Online job, however, is to provide a DBMS environment for users to log into and work with the data, so Online jobs typically run for very long periods of time. To make this possible, an Online CCAIN stream contains a HALT command near the end of the stream, which specifies an operator command that may be used to stop the job. Execution of the Model 204 Online waits at this command until the operator issues the "stop" command, which is usually EOD for End Of Day, or EOJ for End Of Job. System Managers may also issue these commands from a terminal session inside Model 204.
If the correct procedures for stopping an Online are not followed, severe damage can be done to database files, and loss of data can occur. Usually Online jobs are configured to run a recovery step before making the online available for user sessions, and Model 204 recovery will automatically repair a large number of problems resulting from abnormal termination.
It is important to know that, because Model 204 hosts its own terminal services, hundreds, or even thousands, of users can be logged into a Model 204 Online simultaneously. On the console, the operator will see only a very large job consuming significant resources. Without proper training, an operator may see this job as a performance anomaly, and might cancel it, inconveniencing a large number of users and interrupting the day's flow of work. The details of what is happening inside an Online can only be viewed by users with terminal sessions inside the job, via various system-monitoring commands like LOGWHO and variations on the MONITOR command. Highly detailed views of performance characteristics can be analyzed in the Model 204 journal via SirScan and with a system, file and user monitoring tool like SirMon.
Online job specification
This is how a Model 204 Online job is typically built:
//M204ONLN JOB CLASS=A,MSGCLASS=A,NOTIFY=LEN //RUN EXEC PGM=ONLINE,REGION=8M, // TIME=1440,PARM=('SYSOPT=149,LIBUFF=1024,LOBUFF=3000') //STEPLIB DD DSN=M204.RLSE.LOADLIB,DISP=SHR //CCAJRNL DD DSN=M204.JOURNAL,DISP=SHR //CHKPOINT DD DSN=M204.CHKPOINT,DISP=SHR //CCATEMP DD UNIT=3390,SPACE=(TRK,90), // DISP=(NEW,DELETE) //CCASNAP DD SYSOUT=A //SYSMDUMP DD SYSOUT=A //SYSUDUMP DD SYSOUT=A //CCAAUDIT DD SYSOUT=A //CCASTAT DD DSN=M204.CCASTAT,DISP=SHR //CCAGRP DD DSN=M204.CCAGRP,DISP=SHR //CLIENTS DD DSN=M204.FILE.CLIENTS,DISP=SHR //VEHICLES DD DSN=M204.FILE.VEHICLES,DISP=SHR //CLAIMS89 DD DSN=M204.FILE.CLAIMS89,DISP=SHR //CLAIMS90 DD DSN=M204.FILE.CLAIMS90,DISP=SHR //CCASERVR DD UNIT=3380,DISP=(NEW,DELETE), // SPACE=(CYL,5,,CONTIG) //CCAPRINT DD SYSOUT=A //CCAIN DD * NUSERS=9,NSERVS=2,MINBUF=18,MAXBUF=1000, X TERMBUF=5,NFILES=4,NDCBS=4,NDIR=4,SPCORE=50000, X IFAMBS=4000,LRETBL=800,VTAMNAME=M204,CRFSCHNL=M204FULL, X CRIOCHNL=M204PROD,IFAMCHNL=IFAMPROD, X RCVOPT=9,CPMAX=1,CPTIME=30,CPTO=5,CPTQ=5, X LFSCB=7000,LGTBL=500,LSTBL=3000,LVTBL=200, X LOUTPB=3000,NBKPG=5,OUTCCC=80,SERVSIZE=72456 IODEV=7,NOTERM=3,POLLNO=1,SERVSIZE=72456 IODEV=7,POLLNO=2 IODEV=7,POLLNO=3 IODEV=29,NOTERM=2,POLLNO=1 IODEV=29,POLLNO=2 IODEV=11,NOTERM=2,POLLNO=1 IODEV=11,POLLNO=2 IODEV=23 HALT 27,MODEL 204 IS UP AND RUNNING,3,EOD EOD *SLEEP 300 BROADCAST URGENT 1***SYSTEM GOES DOWN IN 5 MINUTES *SLEEP 300 HALT 24,WAIT FOR USERS TO LOGOUT,3,EOJ CHECKPOINT BUMP ALL *SLEEP 300 EOJ
Note the positional continuation-line markers for the first entries in CCAIN. These are required so that all the parameters needed to define the Online environment are read. Also note that the first parameter, NUSERS, matches the number of IODEVs plus 1 (for the User 0 user). It is the presence of NUSERS greater than 1, and the different types of input/output devices, that differentiate a Model 204 Online job from a Batch job.