My 1/2 cents on this... Another way of thinking of scattered -vs- sequential reads is that a scattered read is used when you know up front that you want to read several blocks and know which blocks they are. You can then use a vectored read to do this or farm them all out in parallel using asynchronous read. Sequential reads implies that you need the result of each block before you can determine the next block to read. Therefore you do single block I/O.
Bill --- Jonathan Lewis <[EMAIL PROTECTED]> wrote: > > Well, Tim did say he was making a long story short. > > scattered reads = multiblock reads which are > typically > associated with tablescans, but can be index > fast full > scans. > > sequential reads = single block reads which are > typically > associated with index block reads, table blocks > accessed > as a consequence of index block reads, but can > be > one-off blocks in table scans and index fast > full scans > due to the existence of previously buffered > blocks or > tail-end blocks on extents. > > And then there are cached LOB reads and .... > > Jonathan Lewis > http://www.jlcomp.demon.co.uk > > Author of: > Practical Oracle 8i: Building Efficient Databases > > Next Seminar - Australia - July/August > http://www.jlcomp.demon.co.uk/seminar.html > > Host to 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]> > Date: 25 April 2002 00:21 > > > |> "db file scattered read" (associated with FULL > |> table scans) and "db file sequential > |> read" (associated with indexed scans) > | > |But see, Tuning 101, p. 35, where a "db file > sequential read" is > |investigated and the waits are found to be reads > from a *table*. > | > |And other examples elsewhere, where "db file > scattered read" is found > to be > |associated with reads from an index. > | > > > -- > Please see the official ORACLE-L FAQ: > http://www.orafaq.com > -- > Author: Jonathan Lewis > INET: [EMAIL PROTECTED] > > Fat City Network Services -- (858) 538-5051 FAX: > (858) 538-5051 > San Diego, California -- Public Internet > access / Mailing Lists > -------------------------------------------------------------------- > 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). __________________________________________________ Do You Yahoo!? Yahoo! Games - play chess, backgammon, pool and more http://games.yahoo.com/ -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Bill Pass INET: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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).
