IMDB Cache and transaction logs

Question

Hi,
We have installed the IMDB Cache as part of a proof of concept. We want to cache a large Oracle table (approx 900 million rows) into a read only local cache group and are finding the amount of space taken by transaction logs during the initial cache load operation exceeds the amount of disk space available. Is there a way to prevent transaction logging during the initial cache load? A failure during the initial load is acceptable for us as we can always reload the cache from the base Oracle table. We are using a datastore with 60GB of memory, however, the filesystem available is 273GB less the 120GB for the two datastore backing files, leaving approximately 150GB for transaction logs. To date we have only been able to load approximately 350 millions rows before failing with
5056: The cache operation fails: error_type=<TimesTen Error>, error_code=<802>, error_message: [TimesTen]TT0802: Data store space exhaustedThe datastore attributes we are using are
[EntResPP]
Driver=/app1/oracle/product/11.2.0/TimesTen/ER/lib/libtten.so
DataStore=/prod100/oradata/EntResPP
LogPurge=1
PermSize=60000
TempSize=2000
PLSQL=1
DatabaseCharacterSet=AL32UTF8
OracleNetServiceName=TRAQPP.worldThe command we use to load the cache is
load cache group ro commit every 256 rows parallel 4Thanks
Mark

Answer 1

The replication agent is only involved if you have AWT cache groups or if you are using replication. If this is a standalone datastore with a readonly cache group then it is not necessary (or possible) to run the replication agent.
The error message you mentioned is nothing to do with transaction log space. What has happenned is that the memory allocated ot the permanent data region within the datastore (where table data, indexes etc. reside) has become full (this corresponds to PermSize in your DSN attributes). This means you have not allocated enough memory in TimesTen to hold all the data. Be aware that there is typically significant storage space 'inflation' when caching data. This can range from 2x through to 5x or more. So, if the table data occupies a real 10 GB in oracle it will require between 20 and 50 GB in TimesTen.
It is possible to suppress logging while loading the cache data (or at least it used to be prior to TT 11.2.1 - I haven't tied this in 11.2.1 myself). You'd do this as follows:
1. Stop all application connections etc. to the datastore, stop cache and replication agents. make sure that the datastore is unloaded from memory.
2. Change the value for 'Logging' in the DSN attributes to 0 and connect to the DSN using ttIsql as the instance administrator user.
3. Start the cache agent. from the ttIsql session issue the command:
load cache group ro commit every 0 rows;
You have to use 0 (load entire group as single 'transaction' and you cannot use the 'parallel' clause.
If this fails you may have to manually delete any rows that were loaded since TT cannot rollback.
4. When the load has completed successfully, stop the cache agent and disconnect the ttIsql session.
5. Change Logging back to 1 and reconnect as instance administrator from ttIsql. restart cache agent.
6. Start applications etc. as required.
Note that I would consider this at best a temporary workaround. Really, you need to ensure you have enough disk space to perform the load using logging. Of course, as I mentioned, the error you are getting right now is nothing to do with log disk space...
Chris