Re: Fast access to a BLOB

[Quoted] Do you have an index on the ObjID, or does the code have to do a tablescan to get to the Lob Locator ?

[Quoted] Are your LOBs stored out of line or would such a tablescan have to plough through lots of chained rows of LOB data ?

[Quoted] What is the Oracle block size - is it engineered to be appropriate to the LOB size ?

--

Jonathan Lewis
Yet another Oracle-related web site: www.jlcomp.demon.co.uk

Matthias Späth wrote in message <7m52il$2m6t$1_at_news.karlsruhe.punkt.de>...


>Hi,

>

>how can I tune the access to a BLOB. At this time I use this Pro*C/C++


Code:


>(this code needs about 1 second for a BLOB of less then 10k in a table of 3


>columns (2 VARCHAR(256) and a BLOB) and about 10000 rows !!!)

>

>EXEC SQL AT :conn ALLOCATE :blob;

>EXEC SQL AT :conn SELECT data INTO :blob FROM archivtab WHERE objID=:obj;

>EXEC SQL AT :conn LOB DESCRIBE :blob GET LENGTH INTO :length;

>if (length == 0) return -1;

>*ptr=malloc((unsigned int)length);

>tmp=*ptr;

>

>do

>{

>  amt=length>32000?32000:length;

>  buffer.len=amt;

>

>  EXEC SQL AT :conn LOB READ :amt FROM :blob AT :offset INTO :buffer;

>

>  memmove(tmp,buffer.arr,amt);

>  tmp+=32000;

>  length-=32000;

>  offset+=32000;

>} while (length>0);

>

>EXEC SQL AT :conn FREE :blob;

>

>