What will be the diff.between Custiomizing(C),Client dependent(E) in BSI System

HI Experts,Can you just clarify in this two components or table names used how it wil be helpful to us. When we have to use these two in updation of taxation updates(TUB)-Tax Updations Bulletin.
So, please give me clarity about these two.
Thanks&Regards
Rajeshwari

Hi
Customizing entries are those which are created by customer himself not delivered via TUBS.If the tables where you have created custom entries are having any new table delivered care must be taken not to import the whole cumulative transport which will then overwrite your custom entries. Custom entries ware not in client 000 they only reside in your development system
Easiet way to decide if a table is client dependent or client independent is to check if it has client as one of the kep field.If it has then it is a client dependent else it is client independent
Hope this makes sense
Regards
Ajay

Similar Messages

What exactly is the diff between main window and variable window

what exactly is the diff between main window and variable window in SAP script?

hi,
MAIN WINDOW :- In a main window you display text and data, which can cover several pages (flow text). As soon as a main window is completely filled with text and data, the system continues displaying the text in the main window of the next page. It automatically triggers the page break.
You can define only have one window in a form as main window.
The main window must have the same width on each page, but can differ in height.
A page without main window must not call itself as next page, since this would trigger an endless loop. In such a case, the system automatically terminates after three pages.
VARIABLE WINDOW :- The contents of variable windows is processed again for each page, on which the window appears. The system outputs only as much text as fits into the window. Text exceeding the window size is truncated; the system does not trigger a page break. Unlike constant windows, the page windows declared as variable windows may have different sizes on different form pages.
As far as the processing of the window contents is concerned, the system currently treats constant and variable windows alike. The only difference is that constant windows have the same size throughout the form.
hope this will be useful.
If useful then reward points.
with regards,
Syed

What exactly is the diff between client dependant and client independant te

Hi gurus,
What is the diff between client independant and client dependant term.. I initially had a confusion related to client independant and client dependant Transport requests, where else are these words applicable, do they apply to data as well, if so how? any links to help me understand the difference..
regards,
kishore

Hi Kishore,
Client Independant: These objects are not specific to any client. And it is universal which can be viewed,changed across the clients.
Client Dependant: These are the objects can be viewed, changed for the client for which it has been assigned. Other clients do not have access on these objects.
In SAP, all objects are finally stored as tables. "Mandt" is key field which determines whether the object is client dependant or not.
Client Independant transport requests will make the transported objects available across the clients. and Client dependent transport request make the objects available only for the client mentioned by field "Mandt"
Regards,
Dinesh D

What is the diff between general gl a/c, control a/c, reconciliation a/c,

Dear All
what is the diff between general gl a/c, control a/c, reconciliation a/c & offsetting a/c.

Hi,
Normal GL Account is the account where the accounting entries are posted. GL Accounts will be broadly of two categories like Balance Sheet Accounts (Assets & Liabilities) and Profit & Loss Accounts (Income and Expenses).
Reconciliation Accounts are used where a subsidiary ledger is maintained. For example for Customers and Vendors details are maintained in separate ledgers but the control totals are posted in the Reconciliation Account which is part of GL Accounts. Similarly reconciliation accounts are maintained for Assets and Materials also. Further, in case of Customer and Vendor accounts the number of line items will be very high, hence only the totals are updated in GL and line items will be individual ledgers. Basically reconciliation account and control account are similar.
Offsetting Account: In Financial Accounting for every debit there should be a corresponding credit. So when ever any entry posted it will normally hit two GL Accounts. When we look at one line item, we will be interested where the other side of the entry is posted. This entry is the offsetting entry.
If you find this usel, please assign points.
Thanks
Murali.

What is the Diff Between tcodes WE19 in XI and WE19 in r/3 sys

Hi all,
Can anyone tell me
What is the Diff Between tcodes WE19 in XI and WE19 in r/3 sys?
one more question I have a File>XI->IDOC scenario
the file is picked up from the sender sys
but not posted the IDOC to the receiver sys
I need to post that particular record to r/3 sys can any tell me how to post the record.
Thanks
Sai.

SAP PI alo have ABAP stack part of PI server, so we will have all trasaction codes in PI too(ECC trasaction codes),the use of WE 19 in ECC to reprocess IDoc to external partner system.
WE 19 tx in PI also same purpose if you are using PI ABAP stack for creating and processing IDoc's,but we never use it.
You hav to build mapping logic to suppress unwated data and create IDoc in ECC.
Regards,
Raj

Whats the diff between express and pro??

Just wondering what the main diff between the two are. I've used pro at school, but cant afford to get it at home. Will i still be able to use the same audio instruments like the same synths and plug ins??? Also, would i be able to run the program on a mac mini (top of the line)?

Matt Mac 63, "Whats the diff between express and pro??" #5, 10:33pm Oct 18, 2005 CDT
All I was saying is that if a person can afford to get Pro, they definitely should. The difference in features adds up to at least the difference in price, if not very much more.
Having said that, Express is good value compared to most other DAW software at that pricepoint, but it is only intended as a 'Lite' version.
Some examples, off the top of my head, of differences not made really clear in the comparison list.
Input Objects:
In Pro you can use Input Objects to monitor incoming signal without rec-enabling a track. That doesn't sound much, on the face of it, but what it means is you can use external FX units (hardware) as inserts in tracks (or busses) just like plugins, and bounce them with the mix. it also means you acn monitor what you are playing into Logic Pro with plugin FX applied, but record dry so you can hear your guitar with the reverb, or whatever, but still have the recorded dry signal so you can change the FX settings later.
Pro has some very handy environment objects. The main one being the Trabsformer object. But also another extremely useful object is TouchTracks.
If you've ever played with Ableton Live you would have noticed you can triger clips with the keyboard in all different ways (loop, gate loop, one shot etc.) Well TouchTracks does that with MIDI regions.(I have a feeling that feature in Live was modeled after Logic's TouchTracks' as it is incredibly similar.)
They are only a few examples of a whole range of differences. If all the differences were itemized in the 'comparison chart' it would be about 3 pages long.
All I am saying is, don't take the comparison chart as the definitive list of differences.
yes, Express is a good basic tool and you can do a lot with it, with some imagination.
The SOS author's claim that:
you're paying less than a third of the price of Logic Pro and getting over 90 percent of the functionality."
is not true in totality.
It may be true to someone who has never dabbled in audio software before, because it takes literally years to become fully conversant with every function in Logic Pro, and no-one uses absolutely everything.
But for serious users, who have big demands, in my opinion, Express is less than 30% of Pro's functionality.

Hi guru's what is the diff between for all entries & joins

hi guru's what is the diff between for all entries & joins

Hi Vasu,
Joins are used to fetch data fast from Database tables:
Tables are joined with the proper key fields to fetch the data properly.
If there are no proper key fields between tables don't use Joins;
Important thing is that don't USE JOINS FOR CLUSTER tableslike BSEG and KONV.
Only use for Transparenmt tables.
You can also use joins for the database VIews to fetch the data.
JOINS
... FROM tabref1 [INNER] JOIN tabref2 ON cond
Effect
The data is to be selected from transparent database tables and/or views determined by tabref1 and tabref2. tabref1 and tabref2 each have the same form as in variant 1 or are themselves Join expressions. The keyword INNER does not have to be specified. The database tables or views determined by tabref1 and tabref2 must be recognized by the ABAP Dictionary.
In a relational data structure, it is quite normal for data that belongs together to be split up across several tables to help the process of standardization (see relational databases). To regroup this information into a database query, you can link tables using the join command. This formulates conditions for the columns in the tables involved. The inner join contains all combinations of lines from the database table determined by tabref1 with lines from the table determined by tabref2, whose values together meet the logical condition (join condition) specified using ON>cond.
Inner join between table 1 and table 2, where column D in both tables in the join condition is set the same:
Table 1 Table 2
A
B
C
D
D
E
F
G
H
a1
b1
c1
1
1
e1
f1
g1
h1
a2
b2
c2
1
3
e2
f2
g2
h2
a3
b3
c3
2
4
e3
f3
g3
h3
a4
b4
c4
3
|--|||--|
Inner Join
A
B
C
D
D
E
F
G
H
a1
b1
c1
1
1
e1
f1
g1
h1
a2
b2
c2
1
1
e1
f1
g1
h1
a4
b4
c4
3
3
e2
f2
g2
h2
|--||||||||--|
Example
Output a list of all flights from Frankfurt to New York between September 10th and 20th, 2001 that are not sold out:
DATA: DATE LIKE SFLIGHT-FLDATE,
CARRID LIKE SFLIGHT-CARRID,
CONNID LIKE SFLIGHT-CONNID.
SELECT FCARRID FCONNID F~FLDATE
INTO (CARRID, CONNID, DATE)
FROM SFLIGHT AS F INNER JOIN SPFLI AS P
ON FCARRID = PCARRID AND
FCONNID = PCONNID
WHERE P~CITYFROM = 'FRANKFURT'
AND P~CITYTO = 'NEW YORK'
AND F~FLDATE BETWEEN '20010910' AND '20010920'
AND FSEATSOCC < FSEATSMAX.
WRITE: / DATE, CARRID, CONNID.
ENDSELECT.
If there are columns with the same name in both tables, you must distinguish between them by prefixing the field descriptor with the table name or a table alias.
Note
In order to determine the result of a SELECT command where the FROM clause contains a join, the database system first creates a temporary table containing the lines that meet the ON condition. The WHERE condition is then applied to the temporary table. It does not matter in an inner join whether the condition is in the ON or WHEREclause. The following example returns the same solution as the previous one.
Example
Output of a list of all flights from Frankfurt to New York between September 10th and 20th, 2001 that are not sold out:
DATA: DATE LIKE SFLIGHT-FLDATE,
CARRID LIKE SFLIGHT-CARRID,
CONNID LIKE SFLIGHT-CONNID.
SELECT FCARRID FCONNID F~FLDATE
INTO (CARRID, CONNID, DATE)
FROM SFLIGHT AS F INNER JOIN SPFLI AS P
ON FCARRID = PCARRID
WHERE FCONNID = PCONNID
AND P~CITYFROM = 'FRANKFURT'
AND P~CITYTO = 'NEW YORK'
AND F~FLDATE BETWEEN '20010910' AND '20010920'
AND FSEATSOCC < FSEATSMAX.
WRITE: / DATE, CARRID, CONNID.
ENDSELECT.
Note
Since not all of the database systems supported by SAP use the standard syntax for ON conditions, the syntax has been restricted. It only allows those joins that produce the same results on all of the supported database systems:
Only a table or view may appear to the right of the JOIN operator, not another join expression.
Only AND is possible in the ON condition as a logical operator.
Each comparison in the ON condition must contain a field from the right-hand table.
If an outer join occurs in the FROM clause, all the ON conditions must contain at least one "real" JOIN condition (a condition that contains a field from tabref1 amd a field from tabref2.
Note
In some cases, '*' may be specified in the SELECT clause, and an internal table or work area is entered into the INTO clause (instead of a list of fields). If so, the fields are written to the target area from left to right in the order in which the tables appear in the FROM clause, according to the structure of each table work area. There can then be gaps between table work areas if you use an Alignment Request. For this reason, you should define the target work area with reference to the types of the database tables, not simply by counting the total number of fields. For an example, see below:
Variant 3
... FROM tabref1 LEFT [OUTER] JOIN tabref2 ON cond
Effect
Selects the data from the transparent database tables and/or views specified in tabref1 and tabref2. tabref1 und tabref2 both have either the same form as in variant 1 or are themselves join expressions. The keyword OUTER can be omitted. The database tables or views specified in tabref1 and tabref2 must be recognized by the ABAP-Dictionary.
In order to determine the result of a SELECT command where the FROM clause contains a left outer join, the database system creates a temporary table containing the lines that meet the ON condition. The remaining fields from the left-hand table (tabref1) are then added to this table, and their corresponding fields from the right-hand table are filled with ZERO values. The system then applies the WHERE condition to the table.
Left outer join between table 1 and table 2 where column D in both tables set the join condition:
Table 1 Table 2
A
B
C
D
D
E
F
G
H
a1
b1
c1
1
1
e1
f1
g1
h1
a2
b2
c2
1
3
e2
f2
g2
h2
a3
b3
c3
2
4
e3
f3
g3
h3
a4
b4
c4
3
|--|||--|
Left Outer Join
A
B
C
D
D
E
F
G
H
a1
b1
c1
1
1
e1
f1
g1
h1
a2
b2
c2
1
1
e1
f1
g1
h1
a3
b3
c3
2
NULL
NULL
NULL
NULL
NULL
a4
b4
c4
3
3
e2
f2
g2
h2
|--||||||||--|
Example
Output a list of all custimers with their bookings for October 15th, 2001:
DATA: CUSTOMER TYPE SCUSTOM,
BOOKING TYPE SBOOK.
SELECT SCUSTOMNAME SCUSTOMPOSTCODE SCUSTOM~CITY
SBOOKFLDATE SBOOKCARRID SBOOKCONNID SBOOKBOOKID
INTO (CUSTOMER-NAME, CUSTOMER-POSTCODE, CUSTOMER-CITY,
BOOKING-FLDATE, BOOKING-CARRID, BOOKING-CONNID,
BOOKING-BOOKID)
FROM SCUSTOM LEFT OUTER JOIN SBOOK
ON SCUSTOMID = SBOOKCUSTOMID AND
SBOOK~FLDATE = '20011015'
ORDER BY SCUSTOMNAME SBOOKFLDATE.
WRITE: / CUSTOMER-NAME, CUSTOMER-POSTCODE, CUSTOMER-CITY,
BOOKING-FLDATE, BOOKING-CARRID, BOOKING-CONNID,
BOOKING-BOOKID.
ENDSELECT.
If there are columns with the same name in both tables, you must distinguish between them by prefixing the field descriptor with the table name or using an alias.
Note
For the resulting set of a SELECT command with a left outer join in the FROM clause, it is generally of crucial importance whether a logical condition is in the ON or WHERE condition. Since not all of the database systems supported by SAP themselves support the standard syntax and semantics of the left outer join, the syntax has been restricted to those cases that return the same solution in all database systems:
Only a table or view may come after the JOIN operator, not another join statement.
The only logical operator allowed in the ON condition is AND.
Each comparison in the ON condition must contain a field from the right-hand table.
Comparisons in the WHERE condition must not contain a field from the right-hand table.
The ON condition must contain at least one "real" JOIN condition (a condition in which a field from tabref1 as well as from tabref2 occurs).
Note
In some cases, '*' may be specivied as the field list in the SELECT clause, and an internal table or work area is entered in the INTO clause (instead of a list of fields). If so, the fields are written to the target area from left to right in the order in which the tables appear in the llen in der FROM clause, according to the structure of each table work area. There can be gaps between the table work areas if you use an Alignment Request. For this reason, you should define the target work area with reference to the types of the database tables, as in the following example (not simply by counting the total number of fields).
Example
Example of a JOIN with more than two tables: Select all flights from Frankfurt to New York between September 10th and 20th, 2001 where there are available places, and display the name of the airline.
DATA: BEGIN OF WA,
FLIGHT TYPE SFLIGHT,
PFLI TYPE SPFLI,
CARR TYPE SCARR,
END OF WA.
SELECT * INTO WA
FROM ( SFLIGHT AS F INNER JOIN SPFLI AS P
ON FCARRID = PCARRID AND
FCONNID = PCONNID )
INNER JOIN SCARR AS C
ON FCARRID = CCARRID
WHERE P~CITYFROM = 'FRANKFURT'
AND P~CITYTO = 'NEW YORK'
AND F~FLDATE BETWEEN '20010910' AND '20010920'
AND FSEATSOCC < FSEATSMAX.
WRITE: / WA-CARR-CARRNAME, WA-FLIGHT-FLDATE, WA-FLIGHT-CARRID,
WA-FLIGHT-CONNID.
ENDSELECT.
And for all entries,
this will help u.
use of FOR ALL ENTRIES:
1. INNER JOIN
DBTAB1 <----
> DBTAB2
It is used to JOIN two DATABASE tables
having some COMMON fields.
2. Whereas
For All Entries,
DBTAB1 <----
> ITAB1
is not at all related to two DATABASE tables.
It is related to INTERNAL table.
3. If we want to fetch data
from some DBTABLE1
but we want to fetch
for only some records
which are contained in some internal table,
then we use for alll entries.
1. simple example of for all entries.
2. NOTE THAT
In for all entries,
it is NOT necessary to use TWO DBTABLES.
(as against JOIN)
3. use this program (just copy paste)
it will fetch data
from T001
FOR ONLY TWO COMPANIES (as mentioned in itab)
4
REPORT abc.
DATA : BEGIN OF itab OCCURS 0,
bukrs LIKE t001-bukrs,
END OF itab.
DATA : t001 LIKE TABLE OF t001 WITH HEADER LINE.
itab-bukrs = '1000'.
APPEND itab.
itab-bukrs = '1100'.
APPEND itab.
SELECT * FROM t001
INTO TABLE t001
FOR ALL ENTRIES IN itab
WHERE bukrs = itab-bukrs.
LOOP AT t001.
WRITE :/ t001-bukrs.
ENDLOOP.
cheers,
Hema.

What is the diff between sd userexits compared to other userexits

hi all,
can anybody tell the diff between sd userexits compared to other userexits
thanks and regards
sareen

Hi
In some of the SD Transactions, Some user exits were default provided in the STd program of that transaction for example Sales order program SAPMV45A has provided with MV45AFZZ and in that you can write most of your user exits
similarly the Delivery Std Program SAPMV50A also has this type of facility
apartfrom these exits these transactions also have other exits which we create/using CMOD/SMOD tcodes
User exits (Function module exits) are exits developed by SAP. The exit is implementerd as a call to a function module. The code for the function module is written by the developer. You are not writing the code directly in the function module, but in the include that is implemented in the function module.
The naming standard of function modules for functionmodule exits is:
EXIT_<program name><3 digit suffix>
The call to a functionmodule exit is implemented as:
CALL CUSTOMER.-FUNCTION <3 digit suffix>
To find a Exit.
Goto Transaction -- Find The Package
SMOD >f4>Use the Package here to Find the Exits In the Package.
Else if you Want to search by Application Area wise ,
There is one more tab to find the Exits in the Respective Application Area.
Implementing the Exit-- CMOD Create ProjectsAssgn your Component .
Now Run ur Transaction to Check if it Triggers.
Thats it..
Suppose you need to find out all the user exits related to a tcode.
1. Execute the Tcode.
2. Open the SAP program.
3. Get the Development Class.
4. Execute Tcode SE84.
5. Open the Node 'Envir. -> Exit Techniques -> 'Customer Exits -> Enhancements'
6. Enter the Development class and execute.
Check out this thread..
The specified item was not found.
1. Type the transaction : system->status-> <PROG. NAME>
2 open SE37 , type EXIT<PROG NAME> and press F4 to get the list of function exits available.
3. Open CMOD utilities->SAP enhancements
EDIT->All selections
4.type the function module name obtained in step 2, in fields 'component name' in 'additional selections' block. and execute.
5. The displayed list contains the enhancements names for the transaction You were looking for.
6. Create a project in CMOD and the code in default include->activate.
http://www.erpgenie.com/sap/abap/code/abap26.htm
which gives the list of exits for a tcode
http://help.sap.com/saphelp_nw04/helpdata/en/bf/ec079f5db911d295ae0000e82de14a/frameset.htm
For information on Exits, check these links
http://www.sap-img.com/abap/a-short-tutorial-on-user-exits.htm
http://www.sapgenie.com/abap/code/abap26.htm
http://www.sap-img.com/abap/what-is-user-exits.htm
http://wiki.ittoolbox.com/index.php/HOWTO:Implement_a_screen_exit_to_a_standard_SAP_transaction
http://www.easymarketplace.de/userexit.php
http://www.sap-img.com/abap/a-short-tutorial-on-user-exits.htm
http://www.sappoint.com/abap/userexit.pdfUser-Exit
http://www.planetsap.com/userexit_main_page.htm
User-Exits
http://www.sap-img.com/abap/a-short-tutorial-on-user-exits.htm
http://www.sap-img.com/ab038.htm
http://www.planetsap.com/userexit_main_page.htm
http://www.sap-basis-abap.com/sapab013.htm
http://sap.ittoolbox.com/documents/popular-q-and-a/user-exits-for-the-transaction-code-migo-3283
These links will help you to learn more on user exits.
http://www.sap-img.com/abap/a-short-tutorial-on-user-exits.htm
http://help.sap.com/saphelp_nw04/helpdata/en/c8/1975cc43b111d1896f0000e8322d00/frameset.htm
http://www.planetsap.com/userexit_main_page.htm
http://www.allsaplinks.com/user_exit.html
www.sap-img.com/abap/what-is-user-exits.htm
Also please check these threads for more details about user exits.
Re: Screen exit
user exit and customer exit
user exit
1. Document on UserExits in FI/CO
http://www.ficoexpertonline.com/downloads/User%20ExitsWPedit.doc
2. Finding User Exits...
http://sap.ionelburlacu.ro/abap/sap2/Other_Useful_Tips.html#Finding_User_Exits
3. List of all User Exits...
http://www.planetsap.com/userexit_main_page.htm
<b>Reward points for useful Answers</b>
Regards
Anji

Hi this pandu can i know what is the diff between pnp &pnpce ldb

hi,
this pandu can i know what is the diff between pnp &pnpce logical database.
thanks and regards,
pandu.

pretty much the same.. except that PNPCE has additional functionality to deal with Concurrent Employment.. PL go through <a href="http://help.sap.com/saphelp_erp2005/helpdata/en/c6/8a15381b80436ce10000009b38f8cf/frameset.htm">SAP Help</a> for more info.
~Suresh

What the diff between Order Acquisition with Order management?

Hi,
What's the diff between them in SAP, thanks!

Hi,
I think Order Acquisition use in module Material management. And Order management use in Sales and Distribution.
Regards,

Hi gurus what is the diff between free & refresh

hi gurus what is the diff between free & refresh

Hii!
FREE f.
Effect
FREE f has the same effect as CLEAR f , namely that a Data object f is reset to the initial value corresponding to its type.
Unlike CLEAR, FREE also releases any resources taken up by the data object f. FREE can also release more resources than CLEAR for table work areas declared using the TABLES statement.
After FREE f, the data object f can be re-addressed at any time. The only condition is that you may need to re-allocate resources to the object.
Note
If f is an internal table with header line (where the name f in a sense has two meanings) the statement FREE f refers to the body of the table, and the statement CLEAR f refers to the header line.
REFRESH itab.
Effect
The internal table itab is reset to its initial state, i.e. all table entries are deleted.
Der Return Code SY-SUBRC is undefined.
Notes
The header entry of a table with a header line remains unchanged. It can be reset to its initial value using CLEAR.
FREE itab can be used to free up the memory allocated to the table.
Note
Performance:
The runtime required to reset an internal table depends on the amount of memory previously occupied by that table.
Resetting a small internal table takes around 15 msn (standard microseconds). Resetting a 200 KB table takes around 400 msn, and a 1 MB table, around 3000 msn.
If the internal table has an index or a hash table (because it was edited using INSERT, DELETE, SORT or COLLECT), the runtime increases slightly, since the index or hash table has to be released as well as the table itself.
Regards
Abhijeet

Whats the diff between Transfered Records and Added Records

Hi
whats the diff between Transfered Records and Added Records in any data target Request Tab.
Regards
ll

Hi.......
Check this.......
What's the difference between Transferred Records and Added Records?
Manage ODS : Difference of Transferred Records and Added Records
Regards,
Debjani......

What is the diff between additive,update ,delete,reverse images

what is the diff between additive,update ,delete,reverse images with an examples.

Hi,
You can read about it here:
http://help.sap.com/saphelp_nw04/helpdata/en/84/81eb588fc211d4b2c90050da4c74dc/content.htm
Hope this helps...

What is the diff. between Access seq. MWST, JTAX & JST1?

Hi,
May I know the diff. between Access seq. MWST, JTAX & JST1,used in tax condition types?
Kind regards,
Kishore

from sap help
An access sequence is a search strategy by means of which the system searches for valid records in various condition tables. It consists of one or more accesses. The sequence of accesses controls the priority of the individual condition records among each other. Through the accesses, the system is told where to look first and where to look next for a valid condition record in each case.
only used for condition record
JST1-sale tax access
JTAX-excise access sequence for condition record maintenance in Fv11
MWST-tax classification
check following link also
[TAXINN Condition;
Regards
Kaials Ugale

What exactly is the difference between enqueue,latch & lock

Can someone explain in simple words (with example if possible) what exactly is the difference between enqueue,latch & lock?
I have gone through documentation & other links,but just not able to figure out the exact & clear difference between these three..
Cheers,
Kunwar

In addition to links provided by Sb and nice explanations by Aman, i would like to add below :
1.Latches and enqueues are lightweight serialization devices used to coordinate multi-user access to
shared data structures, objects and files.
Latches are locks that are held for extremely short periods of time, for example the time it takes to modify
an in-memory data structure. They are used to protect certain memory structures, such as the database
block buffer cache or the library cache in the shared pool (as described in Chapter 2, Architecture). Latches
are typically requested internally in a ‘willing to wait’ mode. This means that if the latch is not available,
the requesting session will sleep for a short period of time and retry the operation later. Other latches may
be requested in an ‘immediate’ mode, meaning that the process will go do something else rather than sit
and wait for the latch to become available. Since many requestors may be waiting for a latch at the same
time, you may see some processes waiting longer than others. Latches are assigned rather randomly, based
on the ‘luck of the draw’, if you will. Whichever session asks for a latch right after it was released will get it.
There is no line of latch waiters, just a ‘mob’ of waiters constantly retrying.
Oracle uses atomic instructions like ‘test and set’ for operating on latches. Since the instructions to set
and free latches are atomic, the operating system itself guarantees that only one process gets it. Since it
is only one instruction, it can be quite fast. Latches are held for short periods of time and provide a
mechanism for clean-up in case a latch holder ‘dies’ abnormally while holding it. This cleaning up
process would be performed by PMON.
Enqueues are another, more sophisticated, serialization device, used when updating rows in a database
table, fro example. They differ from latches in that they allow the requestor to ‘queue up’ and wait for
the resource. With a latch request, the requestor is told right away whether they got the latch or not.
With an enqueue, the requestor will be blocked until they actually attain it. As such, they are not as fast
as a latch can be, but they do provided functionality over and above that which a latch can offer.
Enqueues may be obtained at various levels, so you can have many ‘share’ locks and locks with various
degrees of ‘shareability’.
Source:Expert Oracle Database Architecture by Thomas Kyte
2.Good PPT at http://nocoug.org/download/2001-05/latches.ppt
3.Good PPT by Mark bobak at http://www.mi-oaug.org/Presentations/Understanding%20Locks%20and%20Enqueues.ppt
HTH
Girish Sharma

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