How the line prefetch impact using memeory on oracle.

Support, we have a table whose structure is like (a varchar2 (4000), b varchar2 (4000), b varchar2 (4000), b varchar2 (4000)). If we fill the with row table of maximum length, i.e.: all ranks will be have4 * 4 k = 16 k data. Then set line prefetch (in sqlplus, arraysize) 5K, then for each extraction, oracle will send 16 K * 5 K = 80 M data to the client. My question is: whence these 80 M stored in oracle?

I first thought these 80 m will get PGA/UGA, but my tests show me the UGA and PGA are less than 5 M, that size is not enough to store the data of 80 M. Oracle will store the data in the buffer of the decision-making level operating system once all the data is ready? Such as: get 15 K data, put it in the socket buffer, get the data from 15 K one another, put it in the socket buffer, so there is no need for oracle store these 80 M within the oracle database? But 80 M data is too large for the buffer of the socket.

user646745 wrote:
My question is if the customer will use super great memory if set prefetch too high. The trace file said oracle is occupied on sending data of 5000 lines without interruption. If the customer must have little need of memory to store. My perl above test has confirmed that it takes a lot of memory to the high setting prefetch.

Yes. It depends on how the OCI (Oracle Call Interface) is used. The [Oracle® Call Interface Programmer Guide | http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14250/oci04sql.htm#sthref645] States:

>
In order to minimize the server back and forth and optimise performance, the SPOUT can preload lines of result set when executing a query. You can customize this prefetching by setting an OCI_ATTR_PREFETCH_ROWS or OCI_ATTR_PREFETCH_MEMORY of the statement handle attribute using the OCIAttrSet() function. These attributes are used as follows:

* OCI_ATTR_PREFETCH_ROWS sets the number of lines to be read beforehand. If it is not set, the default value is 1. If the OCIStmtExecute() iters parameter is 0 and prefetching is enabled, lines are buffered during calls to OCIStmtFetch2(). The value of read-ahead can be changed after the execution, as well as between extractions.

* OCI_ATTR_PREFETCH_MEMORY sets the allocated memory to be a prior extraction lines. The application then retrieves lines as much as can fit in this amount of memory.

When both of these attributes are specified, the Prerecupere BEAK of the lines up to the OCI_ATTR_PREFETCH_ROWS limit, unless the limit OCI_ATTR_PREFETCH_MEMORY is reached, in which case the NOZZLE return so many rows than fit in a buffer of size OCI_ATTR_PREFETCH_MEMORY.

By default, the preload is turned on, and the SPOUT recovers an additional line all the time. To enable disable prefetching, define the attributes of the OCI_ATTR_PREFETCH_ROWS and the OCI_ATTR_PREFETCH_MEMORY to zero.
>

Therefore, if either prefetch value is high. client memory use will also increase at the same time. The '+' safer + two methods would be to OCI_ATTR_PREFETCH_MEMORY the value that you specify then a size of buffer extraction absolute memory... whereas the use of OCI_ATTR_PREFETCH_ROWS can cause a heavy memory hit to extract lines very large and in turn use very little memory when you read the small lines.

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