Calculating the storage requirement for the extended common service area

You must calculate the approximate storage requirement for the extended common service area (ECSA).

Before you begin

Determine the values of the following subsystem parameters for use in the calculations:

Procedure

Start of changeTo estimate storage that is needed for ECSA (above the 16-MB line) for each Db2 subsystem, use the following calculations:
  1. Start with 7.5 MB 1 of ECSA storage for the code base.
  2. Add 4 KB for each user. You can use (MAXDBAT-value + CTHREAD-value) × 4 KB. 2
  3. Add 1 KB for each system that is listed as a TCP/IP address or SNA LU name in the communication database (CDB) when this Db2 subsystem is a DRDA requestor. You do not need to count the number of connections between Db2 and these servers.
  4. Add 5 MB for each IRLM subsystem.
    Each IRLM subsystem uses 4 - 5 MB of ECSA when no workload is active and the default trace settings are used. As the workload increases, the ECSA use in IRLM for locking might also increase, depending on the type of requests processed by IRLM.

    For example, if a workload processes many queries or notifies through IFI calls, the ECSA increases depending on the numbers of locks that are held, threads,members in the data sharing group, and so forth. When multiple IFI requests run concurrently, the ability of IRLM to reuse and or release the ECSA storage is reduced. In such scenarios, the ECSA usage by IRLM might go up to 10 MB.

  5. If optional tracing is used for IRLM with the TRACE parameter, add memory for the IRLM optional trace buffers:
    • If TRACE=YES is used, add 1.3 MB.
    • If TRACE=n is used, where n is the number of optional trace buffers, add 512 × n KB.
  6. Start of changeFL 500 Add 8 MB 3 for the instrumentation facility interface (IFI) buffers, as requested by monitoring programs and the standard trace classes for accounting (1, 2, 3, 7, and 8) and statistics (1, 3, 4, 5 and 6).End of change
    If Db2 encounters a shortage of ECSA storage for IFI processing, Db2 can continue processing threads, but trace records might be lost until the ECSA shortage is resolved.
Notes:
  1. If you do not use the distributed data facility (DDF), only 5 MB is required for the code base.
  2. If you also use SNA communication, which is deprecated, add an additional 1 KB for each SNA connection.
  3. Until you first activate function level 500 in Db2 13, you might need as much as an additional 25 MB for IFI buffers as requested by monitoring programs.
End of change

What to do next

Specify this sum or a value that is larger than this sum as the second value of the CSA parameter of the IEASYSxx z/OS® logical PARMLIB member. The logical PARMLIB is usually referred to as SYS1.PARMLIB. Specifying values that are too high is preferable to specifying values that are too low; making your values too low can result in a need to IPL z/OS. For example, if the ECSA size is too small, z/OS places the Db2 global load modules and control blocks for Db2 in CSA below the 16-MB line instead of above it. This can cause problems with coexisting z/OS subsystems.

Distributed threads are represented by z/OS SSRB control blocks that reside in the extended system queue area (ESQA) when they are paused. The amount of storage that is used might vary depending on the z/OS release that is used. Estimate 4 KB of ESQA for every active distributed thread. You can use MAXDBAT-value × 4 KB.