RE: locally managed autoallocate (was: Separate Indexes and Data)
-Original Message- From: Jesse, Rich Sent: Wednesday, October 01, 2003 9:49 AM To: Multiple recipients of list ORACLE-L Subject: RE: locally managed autoallocate (was: Separate Indexes and Data) Theoritically, perhaps, but what if an existing table needs to auto-extend at 1M and all that's left in the table is 16 (or whatever) (blush) Obviously, that's supposed to say left in the tableSPACE. 9.0.1 'unable to allocate extent' C:\Documents and Settings\Niallsqlplus niall/niall SQL*Plus: Release 9.2.0.1.0 - Production on Thu Oct 2 21:59:45 2003 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. Connected to: Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production With the Partitioning, OLAP and Oracle Data Mining options JServer Release 9.2.0.1.0 - Production SQL create tablespace test_auto 2 datafile 'c:\oracle\oradata\home9i\test_auto.dbf' size 1152k 3 extent management local; Tablespace created. SQL create table t1(n number,charcol char(200)) 2 tablespace test_auto 3 ; Table created. SQL select count(*) from dba_extents where segment_name='T1'; COUNT(*) -- 1 SQL begin 2 for i in 1..14 loop 3 execute immediate 'alter table t1 allocate extent'; 4 end loop; 5 end; 6 / PL/SQL procedure successfully completed. SQL analyze table t1 compute statistics; Table analyzed. SQL select count(*) from dba_extents where segment_name='T1'; COUNT(*) -- 15 SQL alter table t1 allocate extent; Table altered. SQL select count(*) from dba_extents where segment_name='T1'; COUNT(*) -- 16 SQL alter table t1 allocate extent; alter table t1 allocate extent * ERROR at line 1: ORA-01653: unable to extend table NIALL.T1 by 128 in tablespace TEST_AUTO SQL select bytes from dba_free_space where tablespace_name='TEST_AUTO'; BYTES -- 65536 SQL create table tX(n number,charcol char(200)) 2 tablespace test_auto; Table created. Niall -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Niall Litchfield 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).
RE: locally managed autoallocate (was: Separate Indexes and Data)
Well, sort of. If I had a 9i DB to play with, I'd try this myself... 1) Create an SMT. 2) Create 50 tables in that TS. 3) Drop every even table just created. 4) Extend one of the remaining tables until you can't. Depending on the size of the TS created and the blocksize, you could have a situation where there's enough freespace in the TS, but not contiguous. Thus, fragmentation. Granted, this is isn't a typical case, but over a year or two, I could see it happening here. Maybe I'll install 9iR2 at home tonite to try this...sigh Rich Rich Jesse System/Database Administrator [EMAIL PROTECTED] Quad/Tech Inc, Sussex, WI USA -Original Message- From: Niall Litchfield [mailto:[EMAIL PROTECTED] Sent: Thursday, October 02, 2003 5:10 PM To: Multiple recipients of list ORACLE-L Subject: RE: locally managed autoallocate (was: Separate Indexes and Data) -Original Message- From: Jesse, Rich Sent: Wednesday, October 01, 2003 9:49 AM To: Multiple recipients of list ORACLE-L Subject: RE: locally managed autoallocate (was: Separate Indexes and Data) Theoritically, perhaps, but what if an existing table needs to auto-extend at 1M and all that's left in the table is 16 (or whatever) (blush) Obviously, that's supposed to say left in the tableSPACE. 9.0.1 'unable to allocate extent' C:\Documents and Settings\Niallsqlplus niall/niall SQL*Plus: Release 9.2.0.1.0 - Production on Thu Oct 2 21:59:45 2003 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. Connected to: Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production With the Partitioning, OLAP and Oracle Data Mining options JServer Release 9.2.0.1.0 - Production SQL create tablespace test_auto 2 datafile 'c:\oracle\oradata\home9i\test_auto.dbf' size 1152k 3 extent management local; Tablespace created. SQL create table t1(n number,charcol char(200)) 2 tablespace test_auto 3 ; Table created. SQL select count(*) from dba_extents where segment_name='T1'; COUNT(*) -- 1 [snip] -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jesse, Rich 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).
RE: locally managed autoallocate (was: Separate Indexes and Data)
-Original Message- From: Jacques Kilchoer [mailto:[EMAIL PROTECTED] Sent: Tuesday, September 30, 2003 7:34 PM To: Multiple recipients of list ORACLE-L Subject: locally managed autoallocate (was: Separate Indexes and Data) Ive read the book. PCTINCREASE is basically set to 100% so the extent sizes double. Thats 'basically' how it works. I have seen some posts on dejanews saying it doesnt necessarily work this way and some people are finding large extent sizes with just a few extents and when tables are dropped this is leading to fragmentation. It hasnt happened to me, but the posts on dejanews were from some pretty good posters. So Im playing conservative. We also had one of the contributors here mention issues. I think Jonathan Lewis has explained the algorithm before, but it's also something that we have investigated here. The algorithm (ignoring some details) is: There will be 4 extent sizes used, 64K, 1M, 8M, 64M As long as object allocation is 1M or less, 64K extent sizes are used, When object allocation is between 1M and 64M, 1M extent sizes are used. When object allocation is between 64M and 1G, 8M extent sizes are used. When object allocation is more than 1G, 64M extent sizes are used. However, when you initially create the object, the extents are determined by figuring out the space allocated to the newly created object taking into account the INITIAL, NEXT, PCTINCREASE, MINEXTENTS storage parameters. So the object might start off with 1M extents instead of starting off with 64K extents. The algorithm is similar to the one outlined above but it is more complicated. The NEXT and PCTINCREASE seem to be ignored after the object is created. e.g. create table ... tablespace locally_managed_autoallocate storage (initial 1M next 512K minextents 15 pctincrease 0) ... ; Initial allocation will be 1M + (15 - 1) * 512K = 8M When you create the table, you will see eight extents, each of one megabyte. There are additional wrinkles, but I don't think the algorithm has bugs. I don't think that there really is fragmentation in the sense that an unused extent will remain unused forever. All extents will be in one of the 4 sizes mentioned above, and all are subject to reuse at some point. Theoritically, perhaps, but what if an existing table needs to auto-extend at 1M and all that's left in the table is 16 (or whatever) 64K chunks. I still maintain that system-managed tablespaces are barely better than DMTs -- fragmentation is still potentially a problem and needs to be monitored. On the flip-side, LMT segments need to be watched too in case they are growing beyond the design of the TS (e.g. more than 1024 or how ever many extents). I'd much rather deal with the latter because it's much less likely to happen unexpectedly in our environment. Rich Rich Jesse System/Database Administrator [EMAIL PROTECTED] Quad/Tech Inc, Sussex, WI USA -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jesse, Rich 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).
RE: locally managed autoallocate (was: Separate Indexes and Data)
-Original Message- From: Jesse, Rich Sent: Wednesday, October 01, 2003 9:49 AM To: Multiple recipients of list ORACLE-L Subject: RE: locally managed autoallocate (was: Separate Indexes and Data) Theoritically, perhaps, but what if an existing table needs to auto-extend at 1M and all that's left in the table is 16 (or whatever) (blush) Obviously, that's supposed to say left in the tableSPACE. 64K chunks. I still maintain that system-managed tablespaces are barely better than DMTs -- fragmentation is still potentially a problem and needs to be monitored. On the flip-side, LMT segments need to be watched too in case they are growing beyond the design of the TS (e.g. more than 1024 or how ever many extents). I'd much rather deal with the latter because it's much less likely to happen unexpectedly in our environment. Rich Rich Rich Jesse System/Database Administrator [EMAIL PROTECTED] Quad/Tech Inc, Sussex, WI USA -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jesse, Rich 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).
locally managed autoallocate (was: Separate Indexes and Data)
Ive read the book. PCTINCREASE is basically set to 100% so the extent sizes double. Thats 'basically' how it works. I have seen some posts on dejanews saying it doesnt necessarily work this way and some people are finding large extent sizes with just a few extents and when tables are dropped this is leading to fragmentation. It hasnt happened to me, but the posts on dejanews were from some pretty good posters. So Im playing conservative. We also had one of the contributors here mention issues. I think Jonathan Lewis has explained the algorithm before, but it's also something that we have investigated here. The algorithm (ignoring some details) is: There will be 4 extent sizes used, 64K, 1M, 8M, 64M As long as object allocation is 1M or less, 64K extent sizes are used, When object allocation is between 1M and 64M, 1M extent sizes are used. When object allocation is between 64M and 1G, 8M extent sizes are used. When object allocation is more than 1G, 64M extent sizes are used. However, when you initially create the object, the extents are determined by figuring out the space allocated to the newly created object taking into account the INITIAL, NEXT, PCTINCREASE, MINEXTENTS storage parameters. So the object might start off with 1M extents instead of starting off with 64K extents. The algorithm is similar to the one outlined above but it is more complicated. The NEXT and PCTINCREASE seem to be ignored after the object is created. e.g. create table ... tablespace locally_managed_autoallocate storage (initial 1M next 512K minextents 15 pctincrease 0) ... ; Initial allocation will be 1M + (15 - 1) * 512K = 8M When you create the table, you will see eight extents, each of one megabyte. There are additional wrinkles, but I don't think the algorithm has bugs. I don't think that there really is fragmentation in the sense that an unused extent will remain unused forever. All extents will be in one of the 4 sizes mentioned above, and all are subject to reuse at some point. -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jacques Kilchoer 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).
Re: locally managed autoallocate (was: Separate Indexes and Data)
Yes, and there is one thing to add: If you do not specify INTIAL, the extent allocation starts with 5 blocks for the intial extent. For 8k, it's 40k, but in an autoallocating LMT extent cannot be smaller then 64k, so it is the amount of the space allocated. The interesting question is: what happens with blocksize-16k? Will there be 64k or two extents of 64k, i.e. 128k? Here is the answer: SQL create tablespace test1 2 datafile '/data/oradata/data/test101.dbf' size 64M reuse 3 autoextend on next 64m maxsize 513M 4 extent management local autoallocate 5 segment space management auto 6 blocksize 16k 7 / Tablespace created. SQL create table a (a number) tablespace test1; Table created. SQL select owner,segment_name,extent_id,blocks 2 from dba_extents 3 where segment_name='A'and tablespace_name='TEST1' 4 and owner=user 5 / OWNER SEGMENT_NA EXTENT_ID BLOCKS -- -- -- -- OPS$MGOGALAA 0 64 16k*64=1M. That means that oracle will allocate a full megabyte for the initial extent. It cannot take 64k, because it's smaller then 5*16k (that number of 5 blocks is hardwired into the RDBMS since time immemorial) and it cannot take two extents because that would, in turn, mean that the initial extent is smaller then 5 blocks. Therefore, it takes 1M. Jonathan Lewis was right. Here is one tecnique for optimizing the disk consumption in such cases: SQL drop tablespace test1 including contents and datafiles; Tablespace dropped. SQL On 2003.09.30 20:34, Jacques Kilchoer wrote: Ive read the book. PCTINCREASE is basically set to 100% so the extent sizes double. Thats 'basically' how it works. I have seen some posts on dejanews saying it doesnt necessarily work this way and some people are finding large extent sizes with just a few extents and when tables are dropped this is leading to fragmentation. It hasnt happened to me, but the posts on dejanews were from some pretty good posters. So Im playing conservative. We also had one of the contributors here mention issues. I think Jonathan Lewis has explained the algorithm before, but it's also something that we have investigated here. The algorithm (ignoring some details) is: There will be 4 extent sizes used, 64K, 1M, 8M, 64M As long as object allocation is 1M or less, 64K extent sizes are used, When object allocation is between 1M and 64M, 1M extent sizes are used. When object allocation is between 64M and 1G, 8M extent sizes are used. When object allocation is more than 1G, 64M extent sizes are used. However, when you initially create the object, the extents are determined by figuring out the space allocated to the newly created object taking into account the INITIAL, NEXT, PCTINCREASE, MINEXTENTS storage parameters. So the object might start off with 1M extents instead of starting off with 64K extents. The algorithm is similar to the one outlined above but it is more complicated. The NEXT and PCTINCREASE seem to be ignored after the object is created. e.g. create table ... tablespace locally_managed_autoallocate storage (initial 1M next 512K minextents 15 pctincrease 0) ... ; Initial allocation will be 1M + (15 - 1) * 512K = 8M When you create the table, you will see eight extents, each of one megabyte. There are additional wrinkles, but I don't think the algorithm has bugs. I don't think that there really is fragmentation in the sense that an unused extent will remain unused forever. All extents will be in one of the 4 sizes mentioned above, and all are subject to reuse at some point. -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jacques Kilchoer 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). -- Mladen Gogala Oracle DBA -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Mladen Gogala 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).
