Connect CDC (SQData) provides two IMS Data Capture agents, the IMS Log Reader and the IMS Transaction Monitor (TM) Exit Captures.
| Attribute | Log Reader | TM Exit |
| Data Capture Latency | Asynchronous | Near-Real-Time |
| Capture Method | Log Miner | Transaction Monitor Exit |
| Unit-of-Work Integrity | Transaction | Transaction |
| Output Datastore Options | TCP/IP | TCP/IP |
| Runtime Parameter Method | SQDCONF | SQDXPARM, SQDCONF |
| Auto-Disable Feature | n/a | Yes |
| Multi-Target Assignment | Yes | Yes |
| Include/Exclude Filters | IMS SSID and optional Filter Exit | Program, Transaction, IMS SSID, Area, HALDB Partition |
| Transaction Include/Exclude | Yes (in Apply Engine and optional Filter Exit) | Yes |
Both IMS Captures have some unique characteristics. The IMS TM Exit Capture agent is a Database Exit and adds NO overhead to IMS Logging. It is the only viable solution for IMS FastPath databases involved in Active/Active Replication, where a Log based capture would quadruple the size of the IMS Log. In a FastPath environment, the Exit can deliver microsecond performance levels in the Real World. Since it is an Exit however, that also means data once published cannot be recaptured. The TM Exit, though highly optimized, also adds some synchronous delays to a single z/OS dispatchable unit (the application task in IMS) to format and write them synchronously, one at a time to a LogStream. The TM Exit in some circumstances provides higher IMS Active/Active replication performance.
The IMS Captures support all types of IMS databases including DEDB, GSAM, HDAM, HIDAM, HISAM, HSAM, PHDAM and PHIDAM.
The Log Capture introduces no capture-related delays while minimally increasing IMS logging. The IMS application is completely independent of capture which runs concurrently but in a separate address space. The Log capture also adds lower LogStream overhead due to the blocking of CDC records. If zIIP processors are used, both log reading and logstream writing are overlapped under yet additional dispatchable units.
Both capture agents utilize z/OS LogStreams, exploiting zIIP processors. Both also use native TCP/IP for all publishing and communication with Engines to deliver superior efficiency and performance.
The tradeoffs can be complicated, may require internal performance testing or be based on other operational priorities. Prior to making that decision, Precisely recommends consultation with support https://www.precisely.com/support to compare your requirements with those of other successful customers and help validate your conclusions.