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TIBCO Rendezvous® 8.7.0

# Memory-Only Mode

Store File

In standard operation, `rvcache` uses the store file to record parameter configuration and for persistent cache storage. Parameter configuration includes the list of cached subjects. Persistent cache storage includes the cached values of those subjects. The required command line parameter `-store` specifies the pathname of the store file.

Memory-Only

In some high-volume situations, writing cached values to the store file can result in an I/O bottleneck. If rvcache I/O presents a problem, you can disable persistent cache storage. The command line parameter `-memory-only` starts `rvcache` in memory-only mode (otherwise, `rvcache` runs in store mode).

Memory-only mode changes the operation of `rvcache` as follows:

| • | When `rvcache` starts, it does not read initial values from the store file. Consequently, `rvcache` starts with an empty cache for all subjects.

| • | `rvcache` keeps cached values only in process memory; it does not write values to the store file.

| • | However, `rvcache` still reads its configuration from the store file at start time, and writes configuration changes to the store file.

Memory-only mode increases the operating speed of `rvcache` at the cost of data persistence. If the process exits, all cached values are lost.

In memory-only mode, you can expect `rvcache` to consume more process memory than in store mode. Since it cannot retrieve infrequently accessed values from the store file, `rvcache` must keep all values in process memory. You must ensure that adequate memory is available.

Note | Switching from store mode to memory-only mode does not automatically erase all initial values from the store file. Even though `rvcache` does not read them, they remain in the store file (which as a result might be larger because of these unnecessary values).
Tip | Since a larger store file can slow `rvcache` initialization, we recommend starting with an empty store file when you begin using memory-only mode. You can use the `dumpXML` command of `tibrvcfg` to dump the configuration of `rvcache` as an XML document. Then use the `matchXML` command to create an empty store file with the required configuration. For details, see Command Line Tool—tibrvcfg in TIBCO Rendezvous Configuration Tools.
Note | After switching from store mode to memory-only mode and back again, you cannot rely on cached values in the store file. Some subject configuration changes can erase the value of a subject as a side effect. Before switching modes, we recommend saving a backup copy of the store file. Alternatively, you can use the `dumpXML` command of `tibrvcfg` to save a backup copy of configuration data before you switch modes. See Command Line Tool—tibrvcfg in TIBCO Rendezvous Configuration Tools.
Tip | When configuring large or complex sets of subjects, the configuration API is more convenient than the browser administration interface; see the Current Value Cache - rvcache section in TIBCO Rendezvous Configuration Tools.

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