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Posted Jan 30, 2004

DB2 Instance and Fast Communication Manager - Part 2

By Marin Komadina

Managing DB2 Fast Communication Manager

In the last article, we discovered the DB2 instance memory structure and fast communication manager, together with all of the DBM parameters influencing memory utilization. In this article we we will continue along those lines with an inside view of FCM tuning and troubleshooting techniques for DB2 running on SUN Solaris.

This article covers:

  • Fast Communication Manager Memory Structure
  • FCM Troubleshooting
  • FCM Tuning
  • Conclusion

Fast Communication Manager Memory Structure

A DB2 partitioned database can be installed using one of the tree following configurations:

  1. Single database partition configuration (SDP) or Single Logical Node (SLN)
  2. Multiple database partition configuration (MDP) or Multiple Logical Nodes (MLN)
  3. Hybrid asymmetric system, having a mix of SDP and MDP database partitions

a.) Single database partition configuration has a defined single database partition per physical host. The global control block for that DB2 instance has the following FCM structures:

  • FCM Connection Entries
  • FCM Message Anchors
  • FCM Request Block

FCM memory structures are separated, having FCM buffers separated from the rest FCM memory structures. The FCM buffer Pool is compromised ofthe FCM Control Block and FCM Buffers. Communication between FCM processes is over UNIX sockets. For each physical node, the memory structure is identical.

b.) Multiple database partition configuration has several database partitions defined per physical host. All memory structures for the Fast Communication Manager are relocated in the FCM Buffer Pool, having the following characteristics:

  • FCM Connection Entries /one per partition
  • FCM Message Anchors /one per partition
  • FCM Request Block /one per partition
  • FCM Buffers /global per node
  • FCM Control Block /global per node

Inter-partition communication on the same host occurs through shared memory (direct) and not over UNIX sockets (FCM deamon). For each physical node, the memory structure is identical.

c.) Hybrid system is very rare, and it is unusual to find it in practice. Principles discussed for SDP as well for MDP configuration are also applicable to mixed systems.

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