ABAP_to_the_Future

Troubleshooting 14.4
send data from a shared memory object on one application server to its counterparts
on the other application servers, so a global invalidation ensures that the
shared memory always matches the database.
Having to reload the data on every application server may seem wasteful, but the
type of information you would want to pu t into shared memory is by definition
the type of information that would hardly ever get changed.
14.4 Troubleshooting
There are two very common problems that arise when working with shared
memory. This section explains how to fix both of them.
14.4.1 Data Inconsistency between Application Servers
If a database read on one application serverreturned a different result than a database
read on another application server, then no one would have faith in the computer
system anymore, and you would have a riot on your hands. With standard
SAP buffered tables, the runtime system ta kes care of making sure that the data
buffer is the same on all application se rvers. With shared memory, you have to
take care of this task yourself.
Section 14.3 talked about ho w to keep the shared memory area in line with the
database and mentioned the way that transactional areas handle this by affecting
all servers. However, many shared memory areas are not defined as transactional,
as they do not mirror an actual database table in its entirety. This section talks
about what to do when you do not have a transactional area.
In the following example, there is a shared memory area to buffer a subset of MARA
records. A user changes the material master record. Even if you have a routine in
a user exit that occurs on save of Transaction MM02 and you send out an invalidate
command, only the shared memory instance on the current application
server gets refreshed, because this is no t a transactional area. This means that if
you have six application servers, then only one has the current data in shared
memory, and the other five have incorrect data. That is a Bad Thing, because anything
reading the shared memory object on the other servers thereafter comes
back with the wrong result, which could have disastrous results.
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