Control blocks

Dump domain anchor block (DUA)
There is one DU anchor block in the system. It is created when DU is initialized, and lasts for the lifetime of the system. It contains information relating to the status of the domain, and pointers to other control blocks.
Dump domain open block.
This contains the data areas associated with the dump data set DCB, namely the ECB, DCB itself, DECB, and the output buffer. It resides below the 16MB line. It is allocated when the data set is opened, and freed when either an explicit close is issued or the end of the current data set is reached and autoswitching is not active.
System dump table (SDT)
Storage for this table is obtained during dump domain preinitialization. The table is then initialized with null table entries. During dump domain initialization, the table is loaded with any values held on the global catalog for system dump codes that were explicitly added during previous CICS® runs. Any system dumps taken before this point in initialization use default dump values (see the CICS Problem Determination Guide for information held for each dump code, and the default values).

Table entries are added during a CICS run either explicitly via CEMT or EXEC CICS commands, or implicitly, with default values, if a dump is requested for which an entry does not exist. These entries can be changed or deleted via CEMT or EXEC CICS commands. Explicitly added entries are written to the global catalog. Further blocks of storage are obtained if necessary as each block fills up. Storage for deleted entries is not reused, because activity on the table is low.

The DU domain anchor block contains pointers to the table, to the first and last active entries in the table, and to the next available entry. The table contains forward and backward pointers so that the table can be accessed in dump code sequence, and additional blocks are chained off the header of the previous block.

Transaction dump table (TDT)
Storage for this table is obtained during dump domain initialization and the table is then loaded with any values held on the global catalog which were explicitly added during previous CICS runs.

Table entries are added during a CICS run either explicitly via CEMT or EXEC CICS commands, or implicitly, with default values, if a dump is requested for which an entry does not exist. These entries can be changed or deleted via CEMT or EXEC CICS commands. Explicitly added entries are written to the global catalog. Further blocks of storage are obtained if necessary as each block fills up. Storage for deleted entries is not reused, because activity on the table is low.

The DU domain anchor (DUA) block contains pointers to the table, to the first and last active entries in the table, and to the next available entry. The table contains forward and backward pointers so that the table can be accessed in dump code sequence, and additional blocks are chained off the header of the previous block.

Browse token table (BTT)
This table holds browse tokens for both system and transaction dump tables. Each browse session started on either dump table is allocated a token that is held in this table, along with the dump code of the last dump table entry obtained by the browse session.

Storage for this table is obtained when the first dump table browse session of a CICS run is started. More storage is obtained when the table is full. Storage for deleted entries is not reused.

The structure of the table is the same as for the dump tables, as shown in Figure 109.

Figure 109. Format of the system and transaction dump tables and browse token table
 This is a technical drawing showing the structure of the system and transaction dump tables and the browse token table.
Notes:
  1. This example is for the transaction dump table, but it also applies to the SDT and the BTT.
  2. The global catalog contained records for dump codes AAAA, BBBB, CCCC, DDDD, and FFFF.
  3. Dump code BBBB has been deleted by an EXEC CICS command, so the NEXT and PREV pointers have been set to zero.
  4. Dump code EEEE has been added during this CICS run and the pointers in entries for DDDD and FFFF adjusted to include EEEE in the correct sequence.
  5. In this example, the first table block is not full, so TDT_NEXT in the block header is zero.

For a detailed description of these control blocks, see the CICS Data Areas manual.

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