SyBase SQL anywhere check if Synchronization is needed?

Question

I have a Sybase SQL Anywhere 11.0.1 database that I am using to sync with an Oracle Consolidated Database.

I know that the SQL Anywhere database keeps track of all of the changes that are made to it so that it knows what to synchronize with the consolidated database. My question is whether or not there is a SQL command that will tell you if the database has changes to sync.

I have a mobile application and I want to show a little flag to the user anytime they have made changes to the handheld that need to be synced. I could just create another table to track that stuff myself but I would much rather just ping the database and ask it if it has changes that need to be synced.

Answer 1

As of SQL Anywhere 17, SAP PM maps to a local Sybase database that contains a TTRANSACTION_UPLOAD table, so to determine if a synchronization is necessary we simply query this table to see if it has any records that need to be sync'd to the HANA consolidation database.

Answer 2

The mobile database doesn't keep track of when the last sync was, the MobiLink server keeps all of that information in the MobiLink tables of the consolidated database.

Since synchronization only transfers necessary information, you could simply initiate a sync. If there's nothing to sync, then very little data will be used by your application.

As a side note, SQL Anywhere has its own SO clone which is monitored by Sybase engineers. If anyone knows for sure, it'll be them.

Answer 3

There's nothing automatic to tell you that there is data to synchronize. In addition to Ben's suggestion, another idea would be to query the SYS.SYSSYNC table at the remote database to get an idea of whether there might be changes. The following statement returns a result set that shows a simple status of your last synchronization :

select ss.site_name, sp.publication_name, ss.log_sent,ss.progress 
from sys.syssync ss, sys.syspublication sp 
where ss.publication_id = sp.publication_id
and ss.publication_id is not null 
and ss.site_name is not null

If progress < log_sent, then the status of the last synchronization is unknown. The last upload may or may not have been applied at the consolidated, because the upload was sent, but no response was received from the MobiLink server. In this case, suggesting a synch isn't a bad idea.

If progress = log_sent, then the last synch was successful. Knowing this, you could check the value of db_property('CurrentRedoPos'), which will return the current log offset of the remote database. If this value is significantly higher than the progress value, there have been many operations applied to the database since the last synchronization, so there's a good chance that there is data to synchronize. There are lots of reasons why even a large difference in progress and db_property('CurrentRedoPos') could result in no actual data needing synchronization.

1. The download from the ML Server is applied by dbmlsync after the progress value at the remote is updated by dbmlsync when the upload is confirmed by the ML Server. Operations applied in the download by dbmlsync are not synchronized back to the ML Server, so the entire offset range could just be the last download that was applied. This could be worked around by tracking the current log offset in the sp_hook_dbmlsync_end hook when the exit code value in the #hook_dict table value is zero. This would tell you the log offset of the database after the download was applied, and you could now compare the saved value with the current log offset.
2. All the operations in the transaction log could be operations on tables that are not synchronized.
3. All the operations in the transaction log could have been rolled back.

My solution is not ideal. Tracking the changes to synchronized tables yourself is the best solution, but I thought I could offer an alternative that might be OK for your needs, with the advantage that you are not triggering an extra action on every operation performed on a synchronized table.