Hi! > i apologize if someone posted this answer(i missed it if you did), but why do cached lobs require writes on the control file?
NOCACHE NOLOGGING LOBs require writes to controlfile, because last nologging operation to a datafile has to be reflected somewhere, for being able to determine which files need to be backed up (since recovery information is not logged for nologging operations). Another option would be to use NOCACHE LOGGING operations, that way no controlfile updates are needed, but I do not recommend it, because NOCACHE LOGGING LOBs require the writing of the whole LOB segment block to redo, even if you modify just one byte in it. CACHE LOGGING is more efficient way in sense of redo generation, that way only changed bytes will be recorded. > and jonathan said that isnt 'necessarily' bad. is that because there isnt alot of I/O? If you don't spend too much time waiting on these events, then yes it's not bad at all. > > so caching lobs are primarily useful for read only or read 'mostly' LOBs? They are useful in many cases, for write LOBs as well in some cases, but the problem is that they always generate redo, which might not be acceptable in high data load environments. IMO, if you can use a combination of disk array with write cache, asynch IO, LOB buffering in client side and write batching, then NOCACHE NOLOGGING LOBs can meet acceptable performance constraints and if you use CACHE READ NOLOGGING LOBs (which seem to be available even from 8.1.6), then your performance will be just fine. Of course, there is always cases with special requirements/contstraints, so YMMAFV (your mileage may, and will vary). Tanel. ----- Original Message ----- To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> Sent: Friday, January 30, 2004 2:49 PM > > From: "Jonathan Lewis" <[EMAIL PROTECTED]> > > Date: 2004/01/30 Fri AM 04:09:25 EST > > To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> > > Subject: Re: [Q] wait time /lob def > > > > > > Tanel, > > > > Oracle 9-2 SQL Ref manual. Lob storage clause. > > The options for lobs on creation are: > > CACHE > > NO CACHE > > CACHE READS > > > > I don't think the last one appeared until 9.2 > > I was wrong about caching only writes, though - > > one of the joys of trying to quote everything from > > memory. > > > > The CACHE READS option means that the > > LOB goes into the buffer cache for reads, but > > not for writes. Pity, really, because I'd quite > > like to see it the other way around. > > > > > > > > Regards > > > > Jonathan Lewis > > http://www.jlcomp.demon.co.uk > > > > The educated person is not the person > > who can answer the questions, but the > > person who can question the answers -- T. Schick Jr > > > > > > Next public appearances: > > Jan 29th 2004 UKOUG Unix SIG - v$ and x$ > > March 2004 Hotsos Symposium - The Burden of Proof > > March 2004 Charlotte NC OUG - CBO Tutorial > > April 2004 Iceland > > > > > > One-day tutorials: > > http://www.jlcomp.demon.co.uk/tutorial.html > > > > > > Three-day seminar: > > see http://www.jlcomp.demon.co.uk/seminar.html > > ____UK___February > > ____UK___June > > > > > > The Co-operative Oracle Users' FAQ > > http://www.jlcomp.demon.co.uk/faq/ind_faq.html > > > > > > ----- Original Message ----- > > To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> > > Sent: Friday, January 30, 2004 12:19 AM > > > > > > > Jonathan, > > > > > > about which version are you talking here? > > > > > > > (You do also have the option in more recent versions > > > > of refining the caching properties so the LOB can be > > > > readcache only, writecache only or read/write cache > > > > or nocache, I believe). > > > > > > I haven't found a way to explicitly set read or write caching for LOBs in > > > system level, although I've done some research on them lately (on 10g as > > > well). Or are you talking about OCI LOB caching here? > > > > > > Tanel. > > > > > > > > > -- > > Please see the official ORACLE-L FAQ: http://www.orafaq.net > > -- > > Author: Jonathan Lewis > > INET: [EMAIL PROTECTED] > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > > San Diego, California -- Mailing list and web hosting services > > --------------------------------------------------------------------- > > To REMOVE yourself from this mailing list, send an E-Mail message > > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > > the message BODY, include a line containing: UNSUB ORACLE-L > > (or the name of mailing list you want to be removed from). You may > > also send the HELP command for other information (like subscribing). > > > > -- > Please see the official ORACLE-L FAQ: http://www.orafaq.net > -- > Author: <[EMAIL PROTECTED] > INET: [EMAIL PROTECTED] > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > San Diego, California -- Mailing list and web hosting services > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB ORACLE-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). > -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Tanel Poder INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
