native barcode generator for crystal reports crack Figure 10-2. Depiction of a low HWM in Objective-C

Creating ECC200 in Objective-C Figure 10-2. Depiction of a low HWM

Figure 10-2. Depiction of a low HWM
DataMatrix Printer In Objective-C
Using Barcode generation for iPhone Control to generate, create Data Matrix 2d barcode image in iPhone applications.
www.OnBarcode.com
Barcode Creator In Objective-C
Using Barcode generation for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
FREELISTS
ECC200 Encoder In Objective-C
Using Barcode creation for iPhone Control to generate, create Data Matrix 2d barcode image in iPhone applications.
www.OnBarcode.com
Barcode Maker In Objective-C
Using Barcode encoder for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
When you use an MSSM tablespace, the FREELIST is where Oracle keeps track of blocks under the HWM for objects that have free space on them.
Generating UPC A In Objective-C
Using Barcode printer for iPhone Control to generate, create UPC Symbol image in iPhone applications.
www.OnBarcode.com
Denso QR Bar Code Encoder In Objective-C
Using Barcode generator for iPhone Control to generate, create QR Code ISO/IEC18004 image in iPhone applications.
www.OnBarcode.com
Note FREELISTS and FREELIST
Print EAN / UCC - 13 In Objective-C
Using Barcode creation for iPhone Control to generate, create EAN13 image in iPhone applications.
www.OnBarcode.com
GTIN - 8 Generator In Objective-C
Using Barcode printer for iPhone Control to generate, create GS1 - 8 image in iPhone applications.
www.OnBarcode.com
this technique.
Decode Data Matrix In VB.NET
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
Draw Data Matrix 2d Barcode In None
Using Barcode maker for Online Control to generate, create ECC200 image in Online applications.
www.OnBarcode.com
GROUPS do not pertain to ASSM tablespaces at all; only MSSM tablespaces use
Draw UPC Code In None
Using Barcode creation for Excel Control to generate, create UPC-A Supplement 2 image in Office Excel applications.
www.OnBarcode.com
Printing Code 128B In Objective-C
Using Barcode generation for iPad Control to generate, create ANSI/AIM Code 128 image in iPad applications.
www.OnBarcode.com
Each object will have at least one FREELIST associated with it, and as blocks are used, they will be placed on or taken off of the FREELIST as needed. It is important to note that only blocks under the HWM of an object will be found on the FREELIST. The blocks that remain above the HWM will be used only when the FREELISTs are empty, at which point Oracle advances the HWM and adds these blocks to the FREELIST. In this fashion, Oracle postpones increasing the HWM for an object until it has to. An object may have more than one FREELIST. If you anticipate heavy INSERT or UPDATE activity on an object by many concurrent users, then configuring more than one FREELIST can have a major positive impact on performance (at the cost of possible additional storage). Having sufficient FREELISTs for your needs is crucial. FREELISTs can be a huge positive performance influence (or inhibitor) in an environment with many concurrent inserts and updates. An extremely simple test can show the benefits of setting FREELISTS correctly. Consider this relatively simple table: ops$tkyte%ORA11GR2> create table t ( x int, y char(50) ) tablespace mssm; Table created.
Reading PDF-417 2d Barcode In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
2D Encoder In Visual Basic .NET
Using Barcode creator for Visual Studio .NET Control to generate, create Matrix image in .NET applications.
www.OnBarcode.com
CHAPTER 10 DATABASE TABLES
Printing GTIN - 128 In Java
Using Barcode generator for Java Control to generate, create EAN / UCC - 14 image in Java applications.
www.OnBarcode.com
Drawing Barcode In Visual Basic .NET
Using Barcode printer for .NET Control to generate, create Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Note mssm in the above example is the name of a tablespace, not a keyword. You may replace it with the name
Recognizing GTIN - 13 In .NET Framework
Using Barcode decoder for Visual Studio .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Generate Barcode In None
Using Barcode drawer for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
of any tablespace you have that uses manual segment space management.
Make Linear 1D Barcode In Visual Studio .NET
Using Barcode generation for Visual Studio .NET Control to generate, create Linear Barcode image in .NET framework applications.
www.OnBarcode.com
EAN13 Encoder In None
Using Barcode encoder for Online Control to generate, create EAN 13 image in Online applications.
www.OnBarcode.com
Using five concurrent sessions, we start inserting into this table like wild. If we measure the systemwide wait events for block-related waits both before and after inserting, we will find large waits, especially on data blocks (trying to insert data). This is frequently caused by insufficient FREELISTs on tables (and on indexes, but we ll cover that in detail in the next chapter Indexes ). I used Statspack for this I took a statspack.snap, executed a script that started the five concurrent SQL*Plus sessions, and waited for them to exit, before taking another statspack.snap. The script these sessions ran was simply: begin for i in 1 .. 100000 loop insert into t values ( i, 'x' ); end loop; commit; end; / exit; Now, this is a very simple block of code, and I m the only user in the database here. I should get the best possible performance. I have plenty of buffer cache configured, my redo logs are sized appropriately, indexes won t be slowing things down, I m running on a machine with two hyperthreaded Xeon CPUs this should run fast. What I discovered afterward, however, is the following: Snapshot Snap Id Snap Time Sessions Curs/Sess Comment ~~~~~~~~ ---------- ------------------ -------- --------- -----------------Begin Snap: 364 17-Mar-10 11:58:24 26 1.7 End Snap: 365 17-Mar-10 11:59:01 24 1.8 Elapsed: 0.62 (mins) Av Act Sess: 4.9 DB time: 3.04 (mins) DB CPU: 1.18 (mins) Top 5 Timed Events Avg %Total ~~~~~~~~~~~~~~~~~~ wait Call Event Waits Time (s) (ms) Time ----------------------------------------- ------------ ----------- ------ -----buffer busy waits 199,708 107 1 53.5 CPU time 70 35.0 db file async I/O submit 44 11 252 5.5 log file parallel write 1,130 9 8 4.5 control file parallel write 56 1 16 .4 ------------------------------------------------------------I collectively waited 107 seconds, or about 21 seconds per session on average, on buffer busy waits. These waits are caused entirely by the fact that there are not enough FREELISTs configured on my table for the type of concurrent activity that is taking place. I can eliminate most of that wait time easily, just by creating the table with multiple FREELISTs
CHAPTER 10 DATABASE TABLES
ops$tkyte@ORA11GR2> create table t ( x int, y char(50) ) 2 storage ( freelists 5 ) tablespace MSSM; Table created. or by altering the object ops$tkyteORA11GR2> alter table t storage ( FREELISTS 5 ); Table altered. You will find that the buffer busy waits goes way down, and the amount of CPU needed (since you are doing less work here; competing for a latched data structure can really burn CPU) also goes down along with the elapsed time: Snapshot Snap Id Snap Time Sessions Curs/Sess Comment ~~~~~~~~ ---------- ------------------ -------- --------- -----------------Begin Snap: 367 17-Mar-10 12:26:50 24 1.3 End Snap: 368 17-Mar-10 12:27:09 22 1.5 Elapsed: 0.32 (mins) Av Act Sess: 4.3 DB time: 1.37 (mins) DB CPU: 0.98 (mins) Top 5 Timed Events Avg %Total ~~~~~~~~~~~~~~~~~~ wait Call Event Waits Time (s) (ms) Time ----------------------------------------- ------------ ----------- ------ -----CPU time 59 59.9 db file async I/O submit 28 15 536 15.3 log file parallel write 752 10 13 9.8 buffer busy waits 17,929 5 0 5.4 cursor: pin S 252 3 11 2.9 What you want to do for a table is try to determine the maximum number of concurrent (truly concurrent) inserts or updates that will require more space. What I mean by truly concurrent is how often you expect two people at exactly the same instant to request a free block for that table. This is not a measure of overlapping transactions; it is a measure of how many sessions are doing inserts at the same time, regardless of transaction boundaries. You want to have about as many FREELISTs as concurrent inserts into the table to increase concurrency. You should just set FREELISTs really high and then not worry about it, right Wrong of course, that would be too easy. When you use multiple FREELISTs, there is a master FREELIST and there are process FREELISTs. If a segment has a single FREELIST, then the master and process FREELISTs are one and the same thing. If you have two FREELISTs, you ll really have one master FREELIST and two process FREELISTs. A given session will be assigned to a single process FREELIST based on a hash of its session ID. Now, each process FREELIST will have very few blocks on it the remaining free blocks are on the master FREELIST. As a process FREELIST is used, it will pull a few blocks from the master FREELIST as needed. If the master FREELIST cannot satisfy the space requirement, then Oracle will advance the HWM and add empty blocks to the master FREELIST. So, over time, the master FREELIST will fan out its storage over the many process FREELISTs (again, each of which has only a few blocks on it). So, each process will use a single process FREELIST. It will not go from process FREELIST to process FREELIST to find space. This means that if you have ten process FREELISTs on a table and the one your process is using exhausts the free buffers on its list, it will not go to another process FREELIST for space so even if the other nine process FREELISTs have five blocks each (45 blocks in total), it will go to the master FREELIST. Assuming the master FREELIST cannot satisfy the request for a free block, it would cause the table to advance the HWM or, if the table s HWM cannot be advanced (all the space is used), to extend (to get another extent). It will then continue to use the space on its FREELIST only (which is no longer empty). There is a tradeoff to be
Copyright © OnBarcode.com . All rights reserved.