I hadn't heard the historic explanation before, so I'll pass on that. As far as the 16MB is concerned - I believe the free memory includes any free space left in the shared_pool_reserved_size.
Since the shared_pool_reserved_size defaults to 5% of the shared_pool_size (I think) it isn't necessarily a surprise that you have 16MB of free memory when your shared_pool size if 320MB. (On the other hand, is the reserved size supposed to be extracted from the main pool, or additional too the main pool) The latching thing is always good for a cop-out. I suspect that v$sgastat would become a major bottle neck if it were always latched and updated in real time. So it seems very likely that it would always be wrong. Regards Jonathan Lewis http://www.jlcomp.demon.co.uk Coming soon a new one-day tutorial: Cost Based Optimisation (see http://www.jlcomp.demon.co.uk/tutorial.html ) Next Seminar dates: (see http://www.jlcomp.demon.co.uk/seminar.html ) ____England______January 21/23 The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html -----Original Message----- To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> Date: 02 January 2003 15:13 Sorry for being so vague, but sometimes I can't help it... It was my understanding in the Oracle7 days that the name of the statistic "free memory" was actually a verb and a noun (i.e. as in "free Nelson Mandela" or "free Willy"), and the number shown alongside this statistic was the cumulative number of bytes freed in the Shared Pool. In other words, every time "N" bytes were freed from the Shared Pool, then the statistic was incremented by "N". At least, this explanation would have accounted for the absurdly huge numbers seen in the V$SGASTAT view for this statistic in those versions and the unreliability in attempting to add the numbers seen in V$SGASTAT to sum to SHARED_POOL_SIZE... Then, sometime in the Oracle8 or Oracle8i timeframe, the meaning of the statistic was changed so that the term "free memory" became what everyone had thought it was, an adjective and a noun (i.e. as in "free beer" or "free time"). A much more useful statistic, certainly... Is this true? If not, is it close? The sum of the information in V$SGASTAT still does not add to SHARED_POOL_SIZE, though (query from v8.1.7.4.0 shown below): SQL> select name, bytes from v$sgastat 2 where pool = 'shared pool'; NAME BYTES -------------------------- ---------- free memory 18208352 miscellaneous 2378964 DML locks 120000 PLS non-lib hp 2096 trigger inform 944 PL/SQL MPCODE 1146204 PL/SQL DIANA 1223360 PX subheap 123476 db_block_hash_buckets 1411080 sessions 377300 KGK heap 48124 State objects 267420 message pool freequeue 124552 Checkpoint queue 885168 enqueue_resources 222912 db_files 370988 KGFF heap 649844 KQLS heap 1709904 dictionary cache 12670280 table definiti 3228 transactions 171264 ksfv subheap 4248 fixed allocation callback 1280 library cache 89490788 simulator trace entries 240000 sql area 187432036 table columns 19520 processes 123380 partitioning d 152976 db_block_buffers 10880000 event statistics per sess 607600 ---------- sum 331067288 SQL> show parameter shared_pool_size NAME TYPE VALUE ------------------- ------- --------- shared_pool_size string 314572800 I'm curious about the 16,494,488 bytes difference. Is it possible that V$SGASTAT is another "unlatched" data structure in memory, allowing errors in the interest of eliminating contention? There are other similar structures in the SGA (i.e. the data structure underlying table MONITORING statistics later flushed to SYS.TABMOD$)... Thanks for any and all insight! -- 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).
