By default, an agent fetches data from the non-Oracle system until it has enough data retrieved to send back to the system. It continues until the number of bytes fetched from the non-Oracle system is equal to or higher than the value of HS_RPC_FETCH_SIZE initialization parameter. In other words, the agent reblocks the data between the agent and Oracle Database in sizes defined by the value of the HS_RPC_FETCH_SIZE initialization parameter.
When the non-Oracle system supports array fetches, you can immediately send the data fetched from the non-Oracle system by the array fetch to Oracle Database without waiting until the exact value of the HS_RPC_FETCH_SIZE initialization parameter is reached. That is, you can stream the data from the non-Oracle system to Oracle Database and disable reblocking by setting the value of the HS_RPC_FETCH_REBLOCKING initialization parameter to OFF.
For example, assume that you set HS_RPC_FETCH_SIZE to 64 kilobytes (KB) and HS_FDS_FETCH_ROWS to 100 rows. Also assume that each row is approximately 600 bytes in size, so that the 100 rows are approximately 60 KB. When the HS_RPC_FETCH_REBLOCKING initialization parameter is set to ON, the agent starts fetching 100 rows from the non-Oracle system.
Because there is only 60 KB of data in the agent, the agent does not send the data back to Oracle Database. Instead, the agent fetches the next 100 rows from the non-Oracle system. Because there is now 120 KB of data in the agent, the first 64 KB can be sent back to Oracle Database.
Now there is 56 KB of data left in the agent. The agent fetches another 100 rows from the non-Oracle system before sending the next 64 KB of data to Oracle Database. By setting the HS_RPC_FETCH_REBLOCKING initialization parameter to OFF, the first 100 rows are immediately sent back to the Oracle database server.