Resolving Process Historian Archiving Inactivity and CCCache Flush Anomalies with WinCC v7.4

In SIMATIC PCS 7 and WinCC v7.4 architectures interfaced with Process Historian 2014, historical process values failing to appear in Process Historian trend graphs until an alarm message is triggered stem from software service pack version mismatches and store-and-forward queue stalls. WinCC v7.4 is strictly incompatible with base Process Historian 2014 RTM/SP1 and requires Process Historian 2014 SP2 with Update 1 or Update 2. Without this patch level, the local CCCache buffer fails to stream cyclic tag packets autonomously, flushing accumulated trend data only when a high-priority alarm packet forces an immediate TCP socket flush.

Process Historian Store-and-Forward and CCCache Queue Architecture

SIMATIC Process Historian (PH) serves as the centralized, long-term historical database for PCS 7 OS Servers. Data transfer between WinCC OS Servers and the Process Historian operates through a decoupled Store-and-Forward architecture:
- WinCC Client Component: On the OS Server, the CCDataMgr process routes logged tags and alarms into local memory-mapped circular queues known as CCCache.
- Process Historian Server Service: The SIMATIC Process Historian Server service on the PH machine polls and extracts data packets from the OS Server over dedicated TCP/IP communication sockets (Port 4222 / 4224).
- Under normal operation, Tag Logging Fast and Slow buffers flush cyclically every few seconds without requiring external triggers.

Root Cause Analysis: Why Alarm Events Force Queue Flushes

When an unpatched software mismatch exists between WinCC v7.4 and Process Historian 2014:
1. Socket Handshake Stall: The cyclic Tag Logging transmission handshake between WinCC v7.4's updated client DLLs and the legacy PH 2014 server daemon fails to trigger autonomous packet dispatch. Data accumulates in the local CCCache queue without transferring to the SQL Server database.
2. Alarm Priority Override: Alarm events generated by ALARM_8P are categorized as high-priority real-time records. When an alarm occurs, WinCC executes an immediate, blocking socket flush command to ensure critical safety messages are delivered to the historian without delay.
3. The Flush Phenomenon: This high-priority alarm flush command sweeps the entire pending TCP transmission buffer, inadvertently dragging along the stalled cyclic Tag Logging packets. Consequently, trend curves appear to update only when alarms are tripped.

Software Compatibility Rules for WinCC v7.4 and Process Historian

To eliminate buffer stalls and restore automated cyclic archiving, the software environment must comply with the official Siemens Compatibility Tool (kompatool):

Incompatible Base: WinCC V7.4 / V7.4 SP1 cannot operate reliably with Process Historian 2014 RTM or Process Historian 2014 SP1.
Mandatory Baseline: WinCC V7.4 strictly requires SIMATIC Process Historian 2014 SP2 (or higher).
Recommended Patch Level: Install Process Historian 2014 SP2 Update 1 or Update 2 alongside the matching WinCC V7.4 Upd 1+ patches on all OS Servers. These updates resolve socket synchronization timeouts and optimize CCCache multi-threading.

Diagnostic Matrix for Process Historian Communication

The following table details diagnostic checks and recovery steps for Process Historian archiving failures:

Diagnostic LayerObservation / Failure SymptomCorrective ActionSoftware Version CheckPH is 2014 RTM or SP1 with WinCC V7.4Upgrade Process Historian to 2014 SP2 with latest UpdateOS Server CCCache QueueCCCache directory growing continuously without shrinkingCheck network port 4222/4224; verify PH service is in state 'Active'Trend DisplayStored values appear only when alarms firePatch PH server to SP2 Upd 2 to resolve cyclic socket flush bugPH Management ConsoleOS Server status indicates 'Disconnected' or 'Error'Verify machine certificates and restart PH Server serviceWindows Event Log'Timeout waiting for database transaction'Verify SQL Server instance HISTORIAN is running and has free disk space

Note: Always verify compatibility in kompatool prior to installing mixed WinCC and PH versions across virtual machines.

Verification

Verify automated historical tag streaming to Process Historian:
1. Ensure Process Historian 2014 SP2 Update 2 is installed on the PH server and OS Server patches are applied.
2. Open the Process Historian Management Console; confirm the OS Server shows status 'Active' with a green indicator.
3. In WinCC Runtime, allow continuous process tag archiving for 15 minutes without triggering any alarms.
4. On the Process Historian or Information Server client, open a trend view for the archived internal tags; verify that trend curves render continuously in real time without waiting for alarm triggers.
5. Inspect the CCCache directory on the OS Server; verify that queue files remain small and flush cyclically.

Limitations and Operational Precautions

Essential rules for Process Historian maintenance:
- Never apply service packs to OS Servers without upgrading the central Process Historian server first; the historian must always be at an equal or higher patch level than connected WinCC servers.
- Ensure network latency between OS Servers and Process Historian is under 5 ms over a dedicated, unthrottled gigabit Terminal Bus.
- Do not manually delete files inside the CCCache directory during active runtime; doing so corrupts the local store-and-forward pointer table.

Engineer FAQ

Why did WinCC 7.3 work without issues on the same Process Historian?

WinCC V7.3 used the legacy client communication library that was natively compatible with PH 2014 RTM/SP1, whereas WinCC V7.4 introduced an updated communication stack requiring PH 2014 SP2.

Where is the CCCache directory located?

The CCCache buffer resides in the OS project directory or in C:\Program Files (x86)\Siemens\WinCC\bin\CCCache\ depending on the installation configuration.

Can Process Historian recover data logged while the network was disconnected?

Yes. The Store-and-Forward mechanism retains buffered data in CCCache and WinCC local segments, transferring all historical points to Process Historian automatically once network connectivity is restored.