Part-1

How we can switch Database Read only to Read/write with out shutdown the database -
alter database startup readonly (for read only mode)
alter databse startup read/write (without shutting it down)
how can we know that which file we r using in a database SPFILE R PFILE? -
If your init.ora is in format initSID.ora that means you are using pfile.
if ARCn process is not working properly and our database is in archievelog mode, then what will happen to our database? it will run r not? Give reason ?
-if arc n fails for any reason after transation activity filled all the rodologs ,oracle server hangs.it is a legal hang becuase when we set the database in arh mode oracle server must not overwrite redo logs unless they are archived.
If any of our back-ground process(mandatory) is not working properly then what will happen to our database? Can we use our database?
-With ORACLE 10g,all six mandatory background process has to run in order to start the database and run it.The instance even will not start,forget about database.This u can check out in alert_SID.log file at OS level(without starting the database).All mandatory background process have to be up and running in order to have a Up n running DB.
Can we use Non-standard block size in temporary tales? -no
what is high water mark in oracle -
The high water mark is divides a segment into used blocks free blocks. Blocks below the high water mark (used blocks) have at least once contained data. This data might have been deleted. Since Oracle knows that blocks beyond the high water mark don't have data, it only reads blocks up to the high water mark in a full table scan. Oracle keeps track of the high water mark for a segment in the segment header. It acts as the boundary between used and unused space. As the amount of data grows due to row inserts and updates, the segment's high water mark grows accordingly. But as row deletes and updates shrink the amount of data in the object, the high water mark is not altered to reflect the segment's new characteristics.
when do we use list partitioning on tables. can we use indexes in temp tables -
by making the table as a partitions internally headers will be created for the table partitions.so that data will be retrieved faster than we use the indexes.ex:if we want 2 retrieve 1,00,000 records of the same table without table partioninng it will take 30 minutes.for this only one header will be used.now divide the table into 4 partitions,than 4 headers will be created and 4,00,000 records will be retrieved in the same 30 mins time.this is the added advantage of table partioning.indexes will be slower than this table partitioning.indexes are helpful if the table contains less number of records only.
Why do we need Virtual IP in Oracle 10G RAC? -
For the internal comunication of all the nodes of RAC.Each nodes have his own vertual IP.
How recyclebin works in Oracle 10G? how long an database objects remain in recyclebin? -
The object in the recycle bin will remain until the space used by it is not reused.Once Oracle wants the space for newer objects or newer rows, it will be reused and we cannot get back the object from recycle bin.
What is the simplest command to create a database -
create database