Will Oracle look into the database buffer cache in this scenario?

hi guys,
say I have a table with a million rows, there are no indexes on it, and I did a
select * from t where t.id=522,000.
About 5 minutes later (while that particular (call it blockA) block is still in the database buffer cache) I do a
select * from t where t.id >400,000 and t.id < 600,000
Would Oracle still pick blockA up from the database buffer cache? if so, how? How would it know that that block is part of our query?
thanks

Without an Index, Oracle would have done a FullTableScan on the first query. The blocks would be very quickly aged out of the buffer cache as they have been retrieved for an FTS on a large table. It is unlikely that block 'A' would be in the buffer_cache after 5minutes.
However, assuming that block 'A' is still in the buffer_cache, how does Oracle know that records for the second query are in block 'A' ? It doesn't. Oracle will attempt another FullTableScan for the second query -- even if, as in the first query -- the resultset returned is only 1 row.
Now, if the table were indexed and rows were being retrieved via the Index, Oracle would use the ROWID to get the "DBA" (DataBlockAddress) and get the hash value of that DBA to identify the 'cache buffers chain' where the block is likely to be found. Oracle will make a read request if the block is not present in the expected location.
Hemant K Chitale
http://hemantoracledba.blogspot.com

Similar Messages

A significant portion of the database buffer cache has been written out to the system paging file.

Hi,
We seem to get this error through SCOM every couple of weeks. It doesn't correlate with the AV updates, so I'm not sure what's eating up the memory. The server has been patched to the latest roll up and service pack. The mailbox servers
have been provisioned sufficiently with more than enough memory. Currently they just slow down until the databases activate on another mailbox server.
A significant portion of the database buffer cache has been written out to the system paging file.
Any ideas?

I've seen this with properly sized servers with very little Exchange load running. It could be a number of different things. Here are some items to check:
Confirm that the server hardware has the latest BIOS, drivers, firmware, etc
Confirm that the Windows OS is running the recommended hotfixes. Here is an older post that might still apply to you
http://blogs.technet.com/b/dblanch/archive/2012/02/27/a-few-hotfixes-to-consider.aspx
http://support.microsoft.com/kb/2699780/en-us
Setup a perfmon to capture data from the server. Look for disk performance, excessive paging, CPU/Processor spikes, and more. Use the PAL tool to collect and analyze the perf data -
http://pal.codeplex.com/
Include looking for other applications or processes that might be consuming system resources (AV, Backup, security, etc)
Be sure that the disk are properly aligned -
http://blogs.technet.com/b/mikelag/archive/2011/02/09/how-fragmentation-on-incorrectly-formatted-ntfs-volumes-affects-exchange.aspx
Check that the network is properly configured for Exchange server. You might be surprise how the network config can cause perf & scom alerts.
Make sure that you did not (improperly) statically set msExchESEParamCacheSizeMax and msExchESEParamCacheSizeMin attributes in Active Directory -
http://technet.microsoft.com/en-us/library/ee832793(v=exchg.141).aspx
Be sure that hyperthreading is NOT enabled -
http://technet.microsoft.com/en-us/library/dd346699(v=exchg.141).aspx#Hyper
Check that there are no hardware issues on the server (RAM, CPU, etc). You might need to run some vendor specific utilities/tools to validate.
Proper paging file configuration should be considered for Exchange servers. You can use the perfmon to see just how much paging is occurring.
These will usually lead you in the right direction. Good Luck!

SCOM reports "A significant portion of the database buffer cache has been written out to the system paging file. This may result in severe performance degradation"

This was discussed here, with no resolution
http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/bb073c59-b88f-471b-a209-d7b5d9e5aa28?prof=required
I have the same issue. This is a single-purpose physical mailbox server with 320 users and 72GB of RAM. That should be plenty. I've checked and there are no manual settings for the database cache. There are no other problems with
the server, nothing reported in the logs, except for the aforementioned error (see below).
The server is sluggish. A reboot will clear up the problem temporarily. The only processes using any significant amount of memory are store.exe (using 53GB), regsvc (using 5) and W3 and Monitoringhost.exe using 1 GB each. Does anyone have
any ideas on this?
Warning ESE Event ID 906.
Information Store (1497076) A significant portion of the database buffer cache has been written out to the system paging file. This may result in severe performance degradation. See help link for complete details of possible causes. Resident cache
has fallen by 213107 buffers (or 11%) in the last 207168 seconds. Current Total Percent Resident: 79% (1574197 of 1969409 buffers)

Brian,
We had this event log entry as well which SCOM picked up on, and 10 seconds before it the Forefront Protection 2010 for Exchange updated all of its engines.
We are running Exchange 2010 SP2 RU3 with no file system antivirus (the boxes are restricted and have UAC turned on as mitigations). We are running the servers primarily as Hub Transport servers with 16GB of RAM, but they do have the mailbox role installed
for the sole purpose of serving as our public folder servers.
So we theroized the STORE process was just grabbing a ton of RAM, and occasionally it was told to dump the memory so the other processes could grab some - thus generating the alert. Up until last night we thought nothing of it, but ~25 seconds after the
cache flush to paging file, we got the following alert:
Log Name:      Application
Source:        MSExchangeTransport
Date:          8/2/2012 2:08:14 AM
Event ID:      17012
Task Category: Storage
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      HTS1.company.com
Description:
Transport Mail Database: The database could not allocate memory. Please close some applications to make sure you have enough memory for Exchange Server. The exception is Microsoft.Exchange.Isam.IsamOutOfMemoryException: Out of Memory (-1011)
   at Microsoft.Exchange.Isam.JetInterop.CallW(Int32 errFn)
   at Microsoft.Exchange.Isam.JetInterop.MJetOpenDatabase(MJET_SESID sesid, String file, String connect, MJET_GRBIT grbit, MJET_WRN& wrn)
   at Microsoft.Exchange.Isam.JetInterop.MJetOpenDatabase(MJET_SESID sesid, String file, MJET_GRBIT grbit)
   at Microsoft.Exchange.Isam.JetInterop.MJetOpenDatabase(MJET_SESID sesid, String file)
   at Microsoft.Exchange.Isam.Interop.MJetOpenDatabase(MJET_SESID sesid, String file)
   at Microsoft.Exchange.Transport.Storage.DataConnection..ctor(MJET_INSTANCE instance, DataSource source).
Followed by:
Log Name:      Application
Source:        MSExchangeTransport
Date:          8/2/2012 2:08:15 AM
Event ID:      17106
Task Category: Storage
Level:         Information
Keywords:      Classic
User:          N/A
Computer:      HTS1.company.com
Description:
Transport Mail Database: MSExchangeTransport has detected a critical storage error, updated the registry key (SOFTWARE\Microsoft\ExchangeServer\v14\Transport\QueueDatabase) and as a result, will attempt self-healing after process restart.
Log Name:      Application
Source:        MSExchangeTransport
Date:          8/2/2012 2:13:50 AM
Event ID:      17102
Task Category: Storage
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:      HTS1.company.com
Description:
Transport Mail Database: MSExchangeTransport has detected a critical storage error and has taken an automated recovery action. This recovery action will not be repeated until the target folders are renamed or deleted. Directory path:E:\EXCHSRVR\TransportRoles\Data\Queue
is moved to directory path:E:\EXCHSRVR\TransportRoles\Data\Queue\Queue.old.
So it seems as if the Forefront Protection 2010 for Exchange inadvertently trigger the cache flush which didn't appear to happen quick or thuroughly enough for the transport service to do what it needed to do, so it freaked out and performed the subsequent
actions.
Do you have any ideas on how to prevent this 906 warning, which cascaded into a transport service outage?
Thanks!

ESE - Event Log Warning: 906 - A significant portion of the database buffer cache has been written out to the system paging file...

Hello -
We have 3 x EX2010 SP3 RU5 nodes in a cross-site DAG.
Multi-role servers with 18 GB RAM [increased from 16 GB in an attempt to clear this warning without success].
We run nightly backups on both nodes at the Primary Site.
Node 1 backup covers all mailbox databases [active & passive].
Node 2 backup covers the Public Folders database.
The backups for each database are timed so they do not overlap.
During each backup we get several of these event log warnings:
Log Name:      Application
Source:        ESE
Date:          23/04/2014 00:47:22
Event ID:      906
Task Category: Performance
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:      EX1.xxx.com
Description:
Information Store (5012) A significant portion of the database buffer cache has been written out to the system paging file. This may result in severe performance degradation.
See help link for complete details of possible causes.
Resident cache has fallen by 42523 buffers (or 27%) in the last 903 seconds.
Current Total Percent Resident: 26% (110122 of 421303 buffers)
We've rescheduled the backups and the warning message occurences just move with the backup schedules.
We're not aware of perceived end-user performance degradation, overnight backups in this time zone coincide with the business day for mailbox users in SEA.
I raised a call with the Microsoft Enterprise Support folks, they had a look at BPA output and from their diagnostics tool. We have enough RAM and no major issues detected.
They suggested McAfee AV could be the root of our problems, but we have v8.8 with EX2010 exceptions configured.
Backup software is Asigra V12.2 with latest hotfixes.
We're trying to clear up these warnings as they're throwing SCOM alerts and making a mess of availability reporting.
Any suggestions please?
Thanks in advance

Having said all that, a colleague has suggested we just limit the amount of RAM available for the EX2010 DB cache
Then it won't have to start releasing RAM when the backup runs, and won't throw SCOM alerts
This attribute should do it...
msExchESEParamCacheSizeMax
http://technet.microsoft.com/en-us/library/ee832793.aspx
Give me a shout if this is a bad idea
Thanks

What else are stored in the database buffer cache?

What else are stored in the database buffer cache except the data blocks read from datafiles?

That is a good idea.
SQL> desc v$BH;
Name                                                                                                      Null?    Type
FILE#                                                                                                              NUMBER
BLOCK#                                                                                                             NUMBER
CLASS#                                                                                                             NUMBER
STATUS                                                                                                             VARCHAR2(10)
XNC                                                                                                                NUMBER
FORCED_READS                                                                                                       NUMBER
FORCED_WRITES                                                                                                      NUMBER
LOCK_ELEMENT_ADDR                                                                                                  RAW(4)
LOCK_ELEMENT_NAME                                                                                                  NUMBER
LOCK_ELEMENT_CLASS                                                                                                 NUMBER
DIRTY                                                                                                              VARCHAR2(1)
TEMP                                                                                                               VARCHAR2(1)
PING                                                                                                               VARCHAR2(1)
STALE                                                                                                              VARCHAR2(1)
DIRECT                                                                                                             VARCHAR2(1)
NEW                                                                                                                CHAR(1)
OBJD                                                                                                               NUMBER
TS#                                                                                                                NUMBERTEMP      VARCHAR2(1)      Y - temporary block
PING      VARCHAR2(1)      Y - block pinged
STALE      VARCHAR2(1)      Y - block is stale
DIRECT      VARCHAR2(1)      Y - direct block
My question is what are temporary block and direct block?
Is it true that some blocks in temp tablespace are stored in the data buffer?

What are all information brought into database buffer cache ?

Hi,
What are all information brought into database buffer cache , when user does any one of operations such as "insert","update", "delete" , "select" ?
Whether the datablock to be modified only brought into cache or entire datablocks of a table brought into cache while doing operations i mentioned above ?
What is the purpose of SQL Area? What are all information brought into SQLArea?
Please explain me the logic behind the questions i asked above.
thanks in advance,
nvseenu

Documentation is your friend. Why not start by
reading the
[url=http://download.oracle.com/docs/cd/B19306_01/serv
er.102/b14220/memory.htm]Memory Architecturechapter.
Message was edited by:
orafad
Hi orafad,
I have learnt MemoryArchitecture .
In that documentation , folowing explanation are given,
The database buffer cache is the portion of the SGA that holds copies of data blocks read from datafiles.
But i would like to know whether all or few datablocks brought into cache.
thanks in advance,
nvseenu

Swapping and Database Buffer Cache size

I've read that setting the database buffer cache size too large can cause swapping and paging. Why is this the case? More memory for sql data would seem to not be a problem. Unless it is the proportion of the database buffer to the rest of the SGA that matters.

Well I am always a defender of the large DB buffer cache. Setting the bigger db buffer cache alone will not in any way hurt Oracle performance.
However ... as the buffer cache grows, the time to determine 'which blocks
need to be cleaned' increases. Therefore, at a certain point the benefit of a
larger cache is offset by the time to keep it sync'd to the disk. After that point,
increasing buffer cache size can actually hurt performance. That's the reason why Oracle has checkpoint.
A checkpoint performs the following three operations:
1. Every dirty block in the buffer cache is written to the data files. That is, it synchronizes the datablocks in the buffer cache with the datafiles on disk.
It's the DBWR that writes all modified databaseblocks back to the datafiles.
2. The latest SCN is written (updated) into the datafile header.
3. The latest SCN is also written to the controlfiles.
The following events trigger a checkpoint.
1. Redo log switch
2. LOG_CHECKPOINT_TIMEOUT has expired
3. LOG_CHECKPOINT_INTERVAL has been reached
4. DBA requires so (alter system checkpoint)

LRU and CKPTQ in database buffer cache

Hi experts out here,
This functionality will work out in Database buffer cache of Oracle 10.2 or greater.
Sources:OTN forums and Concepts 11.2 guide
As per my readings.To improve the funtionality and make it more good Database Bufer cache is divided into several areas which are called workareasNow further
zooming this each workarea will store multiple lists to store the buffers inside the database buffer cache.
Each wrokarea can have one or more then one lists to maintain the wrokordering in there.So the list each workarea will have is LRU list and CKPTQ list.LRU list
is a list of pinned,free and dirty buffers and CKPTQ is a list of Dirty buffers.We can say CKPTQ is a bundled of dirty buffers in low RBA ordering and ready to be flushed from cache to disk.
CKPTQ list is maintained in low RBA ordering.
As being novice let me clear about low RBA and High RBA first
RBA is stored in the block header and will give us the information about when this block is changed and how many times it is changed.
Low RBA : the low RBA is the address of the redo for the first change that was applied to the block since it was last clean,
high RBA : the high RBA is the address of the redo for the most recent change to have been applied to the block.
Now Back to CKPTQ
It can be like this (Pathetic diagram of CKPTQ)
lowRBA==================================High RBA
(Head Of CKPTQ) (Tail Of CKPTQ)
CKPTQ is a list of Dirty buffers.As per RBA concept.The most recent buffer modified is at the tail of CKPTQ.
Now oracle process starts and Try to Get buffer from DB cache if it gets a Buffer it will put a buffer MRU end of the LRU list.and buffer will become the most
recently used.
Now if process cant find a required buffer.then first it will try to find out Free buffer in LRU.And if it finds it its over it will place a datablock from datafile to the
place where free buffer was sitting.(Good enough).
Now if process cant fnd a Free buffer in LRU then First step would be it will find some Dirty buffers from the LRU end of the LRU list and place them on a
CKPTQ(Remeber in low order of RBA it will arrange it in CKPT queue). and now oracle process will take required buffer and place it on the MRU end of LRU list.(Because space has been acclaimed by moving Dirty buffers to CKPTQ).
I am sure that from CKPTQ the buffers(to be more accurate Dirty buffers) will move to datafiles.all the buffers are line up n CKPTQ in lower RBA first manner.But
will be flushed to datafile how and in which manner and what event?
This is what i understand after last three days flicking through blogs,forums and concepts guide.Now what i am missing please clear me out and apart from that
i cant link the following functionalities with this flow..that is
1)How the incremental checkpoint work with this CKPTQ?
2)Now what is that 3 seconds timeout?
(Every 3 seconds DBWR process will wake and find if anything there to write on datafiles for this DBWR will only check CKPTQ).
3)apart form 3 second funda , when CKPTQ the buffers will be moved??(IS it when Process cant find any space in CKPTQ to keep buffers from LRU.ITs a
moment when buffer from CKPTQ will be moved to disk)
4)Can you please relate when control file will be updated with checkpoint so it can reduce recovery time?
To many ques but i am trying to build up the whole process in mind that how it works may be i can be wrong in any phase in any step please correct me up and
take me @ the end of flow..
THANKS
Kamesh

Hi Amansir,
So i m back with my bunch of questions.I cant again ask a single because you know its a flow so i cant end up with single doubt.Thanks for your last reply.
Yes amansir first doubt clear that was buffer will be inserted at MID point for this i got one nice document (PDF)names "All about oracle touch count algorithm by CRAIG A SHALLAHAMER".That was quite nice PDF allabout hot and cold buffer and buffer movments inside the LRU list.I am prettly much clear with that point.Thank you. and Incremental checkpoint i read from Harald.van.Breederode ppt a person from oracle.You have shared it on one of your thread.that was nice reference
flicking through threads i came across term REPL and its variations REPL-AUX (thread was for Oracle 9i).Is this variation REPL-AUX deprecated in 10g So i i am not wrong For each work area two main lists that are LRU and CKPTQ exists??not more than that any other types?
For non-RAC database Thread checkpoint is a Full checkpoint?
I read about the incremental checkpointing Here incremental checkpointing in my words n brief.Incremental Checkpoints means write only some selected buffer from CKPTQ to Datafiles.FROM CKPTQ few Low orders RBA buffers are selected and chekcpointed *(Buffer will be checkpointed on many conditions)* and When the Next checkpoint occurs that buffers are flushed to disk.Now this thing *(Checkpointing few buffers and flushing them to disk)* can be multiple times within three seconds so after 3 seconds *(This is the 3 second concept i was asking in the starting of the thread,Can this time be changed if yes with which parameter)* the checkpoint RBA and Checkpoint*(the point upto which database buffer has flushed to disk)* will be updated in Control file header *(Datafile also)* by CKPT process.So that Checkpoint will be used for Instance recovery purpose.Which can dramatically down the instance recovery time.
every 3 seconds control file is updated with checkpoint and that checkpoint is the point from where we have to start the recovery process in oracle from redo log.I m aware that incremental checkpointing is controlled by Fast_start_mttr_target prarameter and now it is autotuned for >10.2 but the smaller value i will keep the less time my instance will take.
Is above two para right what i understood if wrong correct me??
What i understand is after three seconds it will take some buffers from the CKPTQ ( from low RBA end ) and flush them to disk.apart from this many other conditions are there when Data will be flushed to disk.
1) like CKPTQ is full.
2)Process cant find a free buffer in LRU
3)to advance checkpoint DBWR writes..
Correct me if i m wrong?
THANKS
Kamesh
Edited by: Kamy on May 2, 2011 10:55 PM

WEBUTIL_PG.WRITE_DATA( ) and uploading documents into the database

When we run our Forms application through Forms Builder, with the user account utilized by our actual users, we're able to upload a file into the database using webutil. This particular database user account is restricted to only the tables and packages it needs access to, granting the full SELECT, INSERT, UPDATE, DELETE to the tables, and then EXECUTE on the packages.
However, when our Developers use their personal database accounts, which essentially have SELECT ANY .. EXECUTE ANY ... etc, this upload process is halted within webutil.pll when it calls the database PACKAGE procedure WEBUTIL_PG.WRITE_DATA( ). It just hangs on that step.
When you look in OEM, during that hang the graph is showing high levels of "Network" activity. Just a solid plateau. We can't figure out why the difference between these accounts has an effect. Does someone see a pattern here that we're missing?
Thanks,
--=Chuck

"Still sounds like a permissions issue to me." I know right?
So I logged in as myself. I have DBA privileges in the database. The call to the database package hung for me as well. No error ... just a hung cursor.
As for debugging ... the call to WEBUTIL_PG hangs, when the Forms code gets to that point in the webutil.pll. So we never even get to the database.
Our next step, is to try to recreate the process solely in PL/SQL without webutil.pll, but the code in there is pretty extensive, and teasing out only the pieces we'll need is pretty tricky.

Flushing Database Buffer Cache

I am trying out variants of a SQL statement in an attempt to tune it. Each variant involves joins across a different combination of tables, although some tables are common across all variants. In order to be able to do a valid comparison of the TKPROF outputs for the variants, I believe I need to flush the database buffer cache between variants so that the db block gets, consistent gets and physical reads parameters are true for each variant. By doing this, data retrieved for one variant is not already in the buffer cache for the next variant, thus not influencing the above parameters for the next variant.
Is it possible to flush the buffer cache? The shared pool can be flushed with the ALTER SYSTEM FLUSH SHARED_POOL command. I've searched but have not been able to find an equivalent for the buffer cache. The NOCACHE option to the ALTER TABLE command only pushes retrieved data to the LRU list in the buffer cache, but does not remove it from the buffer cache.
I'm hoping to be able to do this without bouncing the database between variants. It is a development instance, and I have it to myself after hours.

Hi,
I never tried this before, but if you want make a test you can try corrupt the block ID's returned by one of these queries below:
Try corrupt the ID of the block containing the segment header
select dbms_rowid.rowid_block_number(rowid) from hr.regions;
Try corrupt one of the blocks returned by the query, which shows the ID of the block where each row is located
select s.owner,t.ts#,s.header_file,s.header_block
from
v$tablespace t, dba_segments s
where
s.segment_name='REGIONS' and
owner='HR' and
t.name = s.tablespace_name;Legatti
Cheers

Loading class oracle/jpub/runtime/dbws/DbwsProxy into the database

I am trying to create a Database Web Services call-out in PL/SQL, however, encountered error "ORA-29540: class oracle/jpub/runtime/dbws/DbwsProxy does not exist". I followed some steps to load utl_dbws.jar, utl_dbws_jserver.jar and dbwsclient.jar into the database, but still getting the same error saying DbwsProxy class does not exist. This is very frustrating and I do not know how to fix this. I tried to just load DbwsProxy.class into the database and it executed successfully, however, the database is still complaining that oracle/jpub/runtime/dbws/DbwsProxy does not exist. Does anyone has any idea what's going on? Thanks much. I am cracking my brain out here.

This is the error message I received when loading:
The following operations failed
class java/lang/NumberFormatException: creation (createFailed)
class java/lang/Number: creation (createFailed)
class java/lang/Object: creation (createFailed)
class java/lang/String: creation (createFailed)
class java/lang/Long: creation (createFailed)
exiting : Failures occurred during processing
This is the error message I received in the database after loading dbwsclient.jar:
ERROR at line 1:
ORA-29540: class oracle/jpub/runtime/dbws/DbwsProxy does not exist
ORA-06512: at "SYS.UTL_DBWS", line 135
ORA-06512: at "SYS.UTL_DBWS", line 132
ORA-06512: at "MICHELLE.MICH", line 8
ORA-06512: at line 1
So that class is still missing. You were suspecting that this class is not loaded successfully into the database? Is it possible for me to just load that particular class into the database?
Thanks.

Database buffer cache and library cache (order)

hi
after I issue:
select * from employees where employee_id=98
which one is performed by oracle first?
Oracle looks database buffer cache for any block it needs.
If block not found in database buffer cache ;server reads block from datafile and places copy in database buffer cache
OR
parse the sql and look in library cache for same execution plan ,.....

Hi Ricardinho
How does Oracle know which blocks it might need ? Does it need blocks from any indexes or does it only need blocks from a table ?
Do you think it even remotely likely that Oracle will somehow get all the blocks it needs first and then worry about determining an execution plan at some later point in time ?
Cheers
Richard Foote
http://richardfoote.wordpress.com/

Capture Web Cam image in APEX and Upload into the Database

Overview
By using a flash object, you should be able to interface with a usb web cam connected to the client machine. Their are a couple of open source ones that I know about, but the one I chose to go with is by Taboca Labs and is called CamCanvas. This is released under the MIT license, and it is at version 0.2, so not very mature - but in saying that it seems to do the trick. The next part is to upload a snapshot into the database - in this particular implementation, it is achieved by taking a snapshot, and putting that data into the canvas object. This is a new HTML5 element, so I am not certain what the IE support would be like. Once you have the image into the canvas, you can then use the provided function convertToDataURL() to convert the image into a Base64 encoded string, which you can then use to convert into to a BLOB. There is however one problem with the Base64 string - APEX has a limitation of 32k for and item value, so can't be submitted by normal means, and a workaround (AJAX) has to be implemented.
Part 1. Capturing the Image from the Flash Object into the Canvas element
Set up the Page
Required Files
Download the tarball of the webcam library from: https://github.com/taboca/CamCanvas-API-/tarball/master
Upload the necessary components to your application. (The flash swf file can be got from one of the samples in the Samples folder. In the root of the tarball, there is actually a swf file, but this seems to be a different file than of what is in the samples - so I just stick with the one from the samples)
Page Body
Create a HTML region, and add the following:
    <div class="container">
     <object id="iembedflash" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000"
codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=7,0,0,0" width="320" height="240">
          <param name="movie" value="#APP_IMAGES#camcanvas.swf" />
          <param name="quality" value="high" />
          <param name="allowScriptAccess" value="always" />
          <embed allowScriptAccess="always" id="embedflash" src="#APP_IMAGES#camcanvas.swf" quality="high" width="320" height="240"
type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" mayscript="true" />
    </object>
    </div>
<p><a href="javascript:captureToCanvas()">Capture</a></p>
<canvas style="border:1px solid yellow" id="canvas" width="320" height="240"></canvas>That will create the webcam container, and an empty canvas element for the captured image to go into.
Also, have a hidden unprotected page item to store the Base64 code into - I called mine P2_IMAGE_BASE64
HTML Header and Body Attribute
Add the Page HTML Body Attribute as:
onload="init(320,240)"
JavaScript
Add the following in the Function and Global Variable Declarations for the page (mostly taken out of the samples provided)
//Camera relations functions
var gCtx = null;
var gCanvas = null;
var imageData = null;
var ii=0;
var jj=0;
var c=0;
function init(ww,hh){
     gCanvas = document.getElementById("canvas");
     var w = ww;
     var h = hh;
     gCanvas.style.width = w + "px";
     gCanvas.style.height = h + "px";
     gCanvas.width = w;
     gCanvas.height = h;
     gCtx = gCanvas.getContext("2d");
     gCtx.clearRect(0, 0, w, h);
     imageData = gCtx.getImageData( 0,0,320,240);
function passLine(stringPixels) {
     //a = (intVal >> 24) & 0xff;
     var coll = stringPixels.split("-");
     for(var i=0;i<320;i++) {
          var intVal = parseInt(coll);
          r = (intVal >> 16) & 0xff;
          g = (intVal >> 8) & 0xff;
          b = (intVal ) & 0xff;
          imageData.data[c+0]=r;
          imageData.data[c+1]=g;
          imageData.data[c+2]=b;
          imageData.data[c+3]=255;
          c+=4;
     if(c>=320*240*4) {
          c=0;
          gCtx.putImageData(imageData, 0,0);
function captureToCanvas() {
     flash = document.getElementById("embedflash");
     flash.ccCapture();
     var canvEle = document.getElementById('canvas');
     $s('P2_IMAGE_BASE64', canvEle.toDataURL());//Assumes hidden item name is P2_IMAGE_BASE64
     clob_Submit();//this is a part of part (AJAX submit value to a collection) two
}In the footer region of the page (which is just a loading image to show whilst the data is being submitted to the collection [hidden by default]) :<img src="#IMAGE_PREFIX#processing3.gif" id="AjaxLoading"
style="display:none;position:absolute;left:45%;top:45%;padding:10px;border:2px solid black;background:#FFF;" />If you give it a quick test, you should be able to see the webcam feed and capture it into the canvas element by clicking the capture link, in between the two elements - it might through a JS error since the clob_Submit() function does not exist yet.
*Part 2. Upload the image into the Database*
As mentioned in the overview, the main limitation is that APEX can't submit values larger than 32k, which I hope the APEX development team will be fixing this limitation in a future release, the workaround isn't really good from a maintainability perspective.
In the sample applications, there is one that demonstrates saving values to the database that are over 32k, which uses an AJAX technique: see http://www.oracle.com/technetwork/developer-tools/apex/application-express/packaged-apps-090453.html#LARGE.
*Required Files*
From the sample application, there is a script you need to upload, and reference in your page. So you can either install the sample application I linked to, or grab the script from the demonstration I have provided - its called apex_save_large.js.
*Create a New Page*
Create a page to Post the large value to (I created mine as 1000), and create the following process, with the condition that Request = SAVE. (All this is in the sample application for saving large values).declare
     l_code clob := empty_clob;
begin
     dbms_lob.createtemporary( l_code, false, dbms_lob.SESSION );
     for i in 1..wwv_flow.g_f01.count loop
          dbms_lob.writeappend(l_code,length(wwv_flow.g_f01(i)),wwv_flow.g_f01(i));
     end loop;
     apex_collection.create_or_truncate_collection(p_collection_name => wc_pkg_globals.g_base64_collection);
     apex_collection.add_member(p_collection_name => wc_pkg_globals.g_base64_collection,p_clob001 => l_code);
     htmldb_application.g_unrecoverable_error := TRUE;
end;I also created a package for storing the collection name, which is referred to in the process, for the collection name:create or replace
package
wc_pkg_globals
as
g_base64_collection constant varchar2(40) := 'BASE64_IMAGE';
end wc_pkg_globals;That is all that needs to be done for page 1000. You don't use this for anything else, *so go back to edit the camera page*.
*Modify the Function and Global Variable Declarations* (to be able to submit large values.)
The below again assumes the item that you want to submit has an item name of 'P2_IMAGE_BASE64', the condition of the process on the POST page is request = SAVE, and the post page is page 1000. This has been taken srtaight from the sample application for saving large values.//32K Limit workaround functions
function clob_Submit(){
          $x_Show('AjaxLoading')
          $a_PostClob('P2_IMAGE_BASE64','SAVE','1000',clob_SubmitReturn);
function clob_SubmitReturn(){
          if(p.readyState == 4){
                         $x_Hide('AjaxLoading');
                         $x('P2_IMAGE_BASE64').value = '';
          }else{return false;}
function doSubmit(r){
$x('P2_IMAGE_BASE64').value = ''
     flowSelectAll();
     document.wwv_flow.p_request.value = r;
     document.wwv_flow.submit();
}Also, reference the script that the above code makes use of, in the page header<script type="text/javascript" src="#WORKSPACE_IMAGES#apex_save_large.js"></script>Assuming the script is located in workspace images, and not associated to a specific app. Other wise reference #APP_IMAGES#
*Set up the table to store the images*CREATE TABLE "WC_SNAPSHOT"
"WC_SNAPSHOT_ID" NUMBER NOT NULL ENABLE,
"BINARY" BLOB,
CONSTRAINT "WC_SNAPSHOT_PK" PRIMARY KEY ("WC_SNAPSHOT_ID")
create sequence seq_wc_snapshot start with 1 increment by 1;
CREATE OR REPLACE TRIGGER "BI_WC_SNAPSHOT" BEFORE
INSERT ON WC_SNAPSHOT FOR EACH ROW BEGIN
SELECT seq_wc_snapshot.nextval INTO :NEW.wc_snapshot_id FROM dual;
END;
Then finally, create a page process to save the image:declare
v_image_input CLOB;
v_image_output BLOB;
v_buffer NUMBER := 64;
v_start_index NUMBER := 1;
v_raw_temp raw(64);
begin
--discard the bit of the string we dont need
select substr(clob001, instr(clob001, ',')+1, length(clob001)) into v_image_input
from apex_collections
where collection_name = wc_pkg_globals.g_base64_collection;
dbms_lob.createtemporary(v_image_output, true);
for i in 1..ceil(dbms_lob.getlength(v_image_input)/v_buffer) loop
v_raw_temp := utl_encode.base64_decode(utl_raw.cast_to_raw(dbms_lob.substr(v_image_input, v_buffer, v_start_index)));
dbms_lob.writeappend(v_image_output, utl_raw.length(v_raw_temp),v_raw_temp);
v_start_index := v_start_index + v_buffer;
end loop;
insert into WC_SNAPSHOT (binary) values (v_image_output); commit;
end;Create a save button - add some sort of validation to make sure the hidden item has a value (i.e. image has been captured). Make the above conditional for request = button name so it only runs when you click Save (you probably want to disable this button until the data has been completely submitted to the collection - I haven't done this in the demonstration).
Voila, you should have now be able to capture the image from a webcam. Take a look at the samples from the CamCanvas API for extra effects if you wanted to do something special.
And of course, all the above assumed you want a resolution of 320 x 240 for the image.
Disclaimer: At time of writing, this worked with a logitech something or rather webcam, and is completely untested on IE.
Check out a demo: http://apex.oracle.com/pls/apex/f?p=trents_demos:webcam_i (my image is a bit blocky, but i think its just my webcam. I've seen others that are much more crisp using this) Also, just be sure to wait for the progress bar to dissappear before clicking Save.
Feedback welcomed.

Hmm, maybe for some reason you aren't getting the base64 version of the saved image? Is the collection getting the full base64 string? Seems like its not getting any if its no data found.
The javascript console is your friend.
Also, in the example i used an extra page, from what one of the examples on apex packages apps had. But since then, I found this post by Carl: http://carlback.blogspot.com/2008/04/new-stuff-4-over-head-with-clob.html - I would use this technique for submitting the clob, over what I have done - as its less hacky. Just sayin.

Database buffer Cache

Hi Guru,
Can anyone tell me what is the actual definition of Data buffer Cache & Log buffer Cache and how it works in Oracle 10g??
Please
Regards,
Rajeev,India
Edited by: 970371 on Nov 8, 2012 7:06 PM

vlethakula wrote:
Databuffer cache contains the blocks which are read from physical data files.Database buffer cache contains buffers that hold the blocks read from the disk.
Log buffer cahce contains changes made to the database
e.g: You try to update a row, the changes made to that row is written in form of change vectors to Log buffer cache, from there on certail rules(like commit) LGWR background process writes those changes from LOG BUFFER CACHE to redo log files.
The block which is modified in database buffer cache, will be written to physical files by DBWR process after certain rules are met (like checkpoint)The reason that I didn't give the explanation or the links containing the same from the docs that I wanted OP to come up with some sort of his own understanding about the two caches first.
Aman....

About database buffer cache issue

Hi all, for example,a DBBC of 4mb size & there is a 1gb table, How this table will be used in DBBC?

Hi,
The whole table will not be taken to cache, but only the required blocks will be placed for oracle operations and unused blocks will be flushed from cache with LRU algorithm. Googling can provide you huge data on this topic.
Oracle Database Buffer Cache Tips
Thank you!!

Will Oracle look into the database buffer cache in this scenario?

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