Friday, October 26, 2007

FAQ around SAP BW DeltaQueue (RSA7)

Frequently Asked Questions around SAP BW DeltaQueue (RSA7)

What does the number in the 'Total' column in Transaction RSA7 mean?
The 'Total' column displays the number of LUWs that were written in the delta queue and that have not yet been confirmed. The number includes the LUWs of the last delta request (for repetition of a delta request) and the LUWs for the next delta request. A LUW only disappears from the RSA7 display when it has been transferred to the BW System and a new delta request has been received from the BW System.

What is a LUW in the delta queue?
A LUW from the point of view of the delta queue can be an individual document, a group of documents from a collective run or a whole data packet of an application extractor.

Why does the number in the 'Total' column in the overview screen of Transaction RSA7 differ from the number of data records that is displayed when you call the detail view?
The number on the overview screen corresponds to the total of LUWs (see also first question) that were written to the qRFC queue and that have not yet been confirmed. The detail screen displays the records contained in the LUWs. Both, the records belonging to the previous delta request and the records that do not meet the selection conditions of the preceding delta init requests are filtered out. Thus, only the records that are ready for the next delta request are displayed on the detail screen. In the detail screen of Transaction RSA7, a possibly existing customer exit is not taken into account.

Why does Transaction RSA7 still display LUWs on the overview screen after successful delta loading?
Only when a new delta has been requested does the source system learn that the previous delta was successfully loaded to the BW System. Then, the LUWs of the previous delta may be confirmed (and also deleted). In the meantime, the LUWs must be kept for a possible delta request repetition. In particular, the number on the overview screen does not change when the first delta was loaded to the BW System.

Why are selections not taken into account when the delta queue is filled?
Filtering according to selections takes place when the system reads from the delta queue. This is necessary for reasons of performance.

Why is there a DataSource with '0' records in RSA7 if delta exists and has also been loaded successfully?
It is most likely that this is a DataSource that does not send delta data to the BW System via the delta queue but directly via the extractor (delta for master data using ALE change pointers). Such a DataSource should not be displayed in RSA7. This error is corrected with BW 20B Support Package 11.

Do the entries in table ROIDOCPRMS have an impact on the performance of the loading procedure from the delta queue?
The impact is limited. If performance problems are related to the loading process from the delta queue, then refer to the application-specific notes (for example in the CO-PA area, in the logistics cockpit area and so on).
Caution: As of PlugIn 2000.2 patch 3 the entries in table ROIDOCPRMS are as effective for the delta queue as for a full update. Please note, however, that LUWs are not split during data loading for consistency reasons. This means that when very large LUWs are written to the DeltaQueue, the actual package size may differ considerably from the MAXSIZE and MAXLINES parameters.

Why does it take so long to display the data in the delta queue (for example approximately 2 hours)?
With PlugIn 2001.1 the display was changed: the user has the option of defining the amount of data to be displayed, to restrict it, to selectively choose the number of a data record, to make a distinction between the 'actual' delta data and the data intended for repetition and so on.

What is the purpose of function 'Delete data and meta data in a queue' in RSA7? What exactly is deleted?
You should act with extreme caution when you use the deletion function in the delta queue. It is comparable to deleting an InitDelta in the BW System and should preferably be executed there. You do not only delete all data of this DataSource for the affected BW System, but also lose the entire information concerning the delta initialization. Then you can only request new deltas after another delta initialization.
When you delete the data, the LUWs kept in the qRFC queue for the corresponding target system are confirmed. Physical deletion only takes place in the qRFC outbound queue if there are no more references to the LUWs.
The deletion function is for example intended for a case where the BW System, from which the delta initialization was originally executed, no longer exists or can no longer be accessed.

Why does it take so long to delete from the delta queue (for example half a day)?
Import PlugIn 2000.2 patch 3. With this patch the performance during deletion is considerably improved.

Why is the delta queue not updated when you start the V3 update in the logistics cockpit area?
It is most likely that a delta initialization had not yet run or that the the delta initialization was not successful. A successful delta initialization (the corresponding request must have QM status 'green' in the BW System) is a prerequisite for the application data being written in the delta queue.

What is the relationship between RSA7 and the qRFC monitor (Transaction SMQ1)?
The qRFC monitor basically displays the same data as RSA7. The internal queue name must be used for selection on the initial screen of the qRFC monitor. This is made up of the prefix 'BW, the client and the short name of the DataSource. For DataSources whose name is 19 characters long or shorter, the short name corresponds to the name of the DataSource. For DataSources whose name is longer than 19 characters (for delta-capable DataSources only possible as of PlugIn 2001.1) the short name is assigned in table ROOSSHORTN.
In the qRFC monitor you cannot distinguish between repeatable and new LUWs. Moreover, the data of a LUW is displayed in an unstructured manner there.

Why are the data in the delta queue although the V3 update was not started?
Data was posted in background. Then, the records are updated directly in the delta queue (RSA7). This happens in particular during automatic goods receipt posting (MRRS). There is no duplicate transfer of records to the BW system. See Note 417189.

Why does button 'Repeatable' on the RSA7 data details screen not only show data loaded into BW during the last delta but also data that were newly added, i.e. 'pure' delta records?
Was programmed in a way that the request in repeat mode fetches both actually repeatable (old) data and new data from the source system.

I loaded several delta inits with various selections. For which one is the delta loaded?
For delta, all selections made via delta inits are summed up. This means, a delta for the 'total' of all delta initializations is loaded.

How many selections for delta inits are possible in the system?
With simple selections (intervals without complicated join conditions or single values), you can make up to about 100 delta inits. It should not be more.
With complicated selection conditions, it should be only up to 10-20 delta inits.
Reason: With many selection conditions that are joined in a complicated way, too many 'where' lines are generated in the generated ABAP source code which may exceed the memory limit.

I intend to copy the source system, i.e. make a client copy. What will happen with may delta? Should I initialize again after that?
Before you copy a source client or source system, make sure that your deltas have been fetched from the DeltaQueue into BW and that no delta is pending. After the client copy, an inconsistency might occur between BW delta tables and the OLTP delta tables as described in Note 405943. After the client copy, Table ROOSPRMSC will probably be empty in the OLTP since this table is client-independent. After the system copy, the table will contain the entries with the old logical system name which are no longer useful for further delta loading from the new logical system. The delta must be initialized in any case since delta depends on both the BW system and the source system. Even if no dump 'MESSAGE_TYPE_X' occurs in BW when editing or creating an InfoPackage, you should expect that the delta has to be initialized after the copy.

Is it allowed in Transaction SMQ1 to use the functions for manual control of processes?
Use SMQ1 as an instrument for diagnosis and control only. Make changes to BW queues only after informing the BW Support or only if this is explicitly requested in a note for component 'BC-BW' or 'BW-WHM-SAPI'.

Despite of the delta request being started after completion of the collective run (V3 update), it does not contain all documents. Only another delta request loads the missing documents into BW. What is the cause for this "splitting"?
The collective run submits the open V2 documents for processing to the task handler which processes them in one or several parallel update processes in an asynchronous way. For this reason, plan a sufficiently large "safety time window" between the end of the collective run in the source system and the start of the delta request in BW. An alternative solution where this problem does not occur is described in Note 505700.

Despite my deleting the delta init, LUWs are still written into the DeltaQueue?!
In general, delta initializations and deletions of delta inits should always be carried out at a time when no posting takes place. Otherwise, buffer problems may occur: If a user started the internal mode at a time when the delta initialization was still active, he/she posts data into the queue even though the initialization had been deleted in the meantime. This is the case in your system.

In SMQ1 (qRFC Monitor) I have status 'NOSEND'. In the table TRFCQOUT, some entries have the status 'READY', others 'RECORDED'. ARFCSSTATE is 'READ'. What do these statuses mean? Which values in the field 'Status' mean what and which values are correct and which are alarming? Are the statuses BW-specific or generally valid in qRFC?
Table TRFCQOUT and ARFCSSTATE: Status READ means that the record was read once either in a delta request or in a repetition of the delta request. However, this does not mean that the record has successfully reached the BW yet. The status READY in the TRFCQOUT and RECORDED in the ARFCSSTATE means that the record has been written into the DeltaQueue and will be loaded into the BW with the next delta request or a repetition of a delta. In any case only the statuses READ, READY and RECORDED in both tables are considered to be valid. The status EXECUTED in TRFCQOUT can occur temporarily. It is set before starting a DeltaExtraction for all records with status READ present at that time. The records with status EXECUTED are usually deleted from the queue in packages within a delta request directly after setting the status before extracting a new delta. If you see such records, it means that either a process which is confirming and deleting records which have been loaded into the BW is successfully running at the moment, or, if the records remain in the table for a longer period of time with status EXECUTED, it is likely that there are problems with deleting the records which have already been successfully been loaded into the BW. In this state, no more deltas are loaded into the BW. Every other status is an indicator for an error or an inconsistency. NOSEND in SMQ1 means nothing (see note 378903).
The value 'U' in field 'NOSEND' of table TRFCQOUT is discomforting.

The extract structure was changed when the DeltaQueue was empty. Afterwards new delta records were written to the DeltaQueue. When loading the delta into the PSA, it shows that some fields were moved. The same result occurs when the contents of the DeltaQueue are listed via the detail display. Why are the data displayed differently? What can be done?
Make sure that the change of the extract structure is also reflected in the database and that all servers are synchronized. We recommend to reset the buffers using Transaction $SYNC. If the extract structure change is not communicated synchronously to the server where delta records are being created, the records are written with the old structure until the new structure has been generated. This may have disastrous consequences for the delta.
When the problem occurs, the delta needs to be re-initialized.

How and where can I control whether a repeat delta is requested?
Via the status of the last delta in the BW Request Monitor. If the request is RED, the next load will be of type 'Repeat'. If you need to repeat the last load for certain reasons, set the request in the monitor to red manually. For the contents of the repeat see Question 14. Delta requests set to red despite of data being already updated lead to duplicate records in a subsequent repeat, if they have not been deleted from the data targets concerned before.

Are there particular recommendations regarding the data volume the DeltaQueue may grow to without facing the danger of a read failure due to memory problems?
There is no strict limit (except for the restricted number range of the 24-digit QCOUNT counter in the LUW management table - which is of no practical importance, however - or the restrictions regarding the volume and number of records in a database table).
When estimating "smooth" limits, both the number of LUWs is important and the average data volume per LUW. As a rule, we recommend to bundle data (usually documents) already when writing to the DeltaQueue to keep number of LUWs small (partly this can be set in the applications, e.g. in the Logistics Cockpit). The data volume of a single LUW should not be considerably larger than 10% of the memory available to the work process for data extraction (in a 32-bit architecture with a memory volumen of about 1GByte per work process, 100 MByte per LUW should not be exceeded). That limit is of rather small practical importance as well since a comparable limit already applies when writing to the DeltaQueue. If the limit is observed, correct reading is guaranteed in most cases.
If the number of LUWs cannot be reduced by bundling application transactions, you should at least make sure that the data are fetched from all connected BWs as quickly as possible. But for other, BW-specific, reasons, the frequency should not be higher than one DeltaRequest per hour.
To avoid memory problems, a program-internal limit ensures that never more than 1 million LUWs are read and fetched from the database per DeltaRequest. If this limit is reached within a request, the DeltaQueue must be emptied by several successive DeltaRequests. We recommend, however, to try not to reach that limit but trigger the fetching of data from the connected BWs already when the number of LUWs reaches a 5-digit value.

1 comment:

SAP said...

Hi Sathya,
Good collection.,
keep it up !

Seelam Rao