About Oracle Metadata Services MDS

Oracle Metadata Service MDS Performance Tuning 7-5 mds-config

7.5.1 Document Cache

In addition to the main MDS cache, MDS uses a document cache in conjunction with each metadata store to store thumbnail information about metadata documents base document and customization documents in memory. The entry for each document is small 100 bytes and the cache size limit is specified in terms of the number of document entries. MDS calculates an appropriate default size limit for the document cache based on the configured maximum size of the MDS Cache, as follows: ■ If MDS cache is disabled, MDS defaults to having no document cache. ■ If MDS cache is enabled, MDS defaults the document cache size to one document entry per KB of document cache configured. ■ If cache-config is not specified, MDS defaults to 10000 document entries. ■ If MDS cache is set to a very small value, MDS uses a minimum size of 500 for document cache. In general, the defaults should be sufficient in most cases. However, insufficient document cache size may impact performance. Prior to packaging the Enterprise ARchive EAR file, you can explicitly set document cache size by adding this entry to adf-config.xml: metadata-store-usage id=db1 metadata-store … property name = … metadata-store document-cache max-entries=10000 metadata-store-usage The DMS metric IOs Per Document Get visible in Enterprise Manager, see Section 7.7 should be less than 1. If not, consider increasing the document cache size.

7.6 Analyzing Performance Impact from Customization

MDS customization may impact performance at run time.The impact from customization depends on many factors including: Note: MDS cache grows in size as metadata objects are accessed until it hits max-size-kb. After that, objects are removed from the cache to make room as needed on a least recently used LRU basis to make room for new objects. Unless time-to-live TTL is set, the MDS cache continues to occupy the max-size-kb of memory. Note: Document cache is cleared when it exceeds the document-cache max-entries value. To avoid performance issues, consider increasing the document cache size if you receive a notification like the following for example: NOTIFICATION: Document cache DBMetadataStore : MDS Repository connection = exceeds its maximum number of entries NNNN, so the cache is cleared.