Relationship between a data block and latch

Hello Experts,
I have just read an article about indexes and full table scan by Richard Foote. http://richardfoote.wordpress.com/2009/04/16/indexes-on-small-tables-part-i-one-of-the-few/
I thought each block required only one latch for each operation. However, I don't undersand that why a single block required 2 latch? The qoute is the following,
Note that yes indeed, there were 4 consistent gets performed and that none of the consistent gets were the “cheaper” consistent gets examinations. Therefore, the 4 consistent gets used in performing the FTS of the one block table required 4 x 2 = 8 latches.
Can anyone explain the above quote please?
Thanks in advance.

Jonathan Lewis wrote:
Solomon Yakobson wrote:
Read Concepts manual. Database Buffer Cache in particular:Every buffer has an access mode: pinned or free (unpinned).
I hope the manual doesn't use the word "free" as a synonym for "unpinned", since a buffer (header) with state = "free" is one that doesn't hold a copy of a datablock and is therefore immediately available for re-use.
Regards
Jonathan Lewis
Hello Sir,
I have just read Memory Architecture document, buffer states part, I know the meaning of dirty buffers. However, when we just SELECT any table, the corresponding data blocks that read into memory from disk, are they considered as clean buffers? Because as far as I understand from dirty buffers, these are modified buffers. And maybe the manual should have used "clean" instead of "free"?
The database uses a sophisticated algorithm to make buffer access efficient. Pointers to dirty and nondirty buffers exist on the same least recently used (LRU) list, which has a hot end and cold end. A coldbuffer is one that has not been recently used. A hot buffer is frequently accessed and has been recently used
Also the above statement is excerpt from Oracle Memory Architecture document, does the nondirty buffers refer to data blocks that move to the memory in SELECT query?
Thanks a lot for your remarkable thoughts.

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Fazlul Kabir Mahfuz wrote:
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http://help.sap.com/saphelp_srm30/helpdata/en/72/0fe1385bed2815e10000000a114084/content.htm
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jschell wrote:
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[http://en.wikipedia.org/wiki/Heap_(data_structure)]
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>
So to terms.
1. Am I correct that the heap was so named because (perhaps at one point in time), a heap is/was commonly used to track the available memory in the free store?Which 'heap'? The VM one? It is probably named that because the implementors of the Sun VM were familar with how C++ and Smalltalk allocated memory.Okay, but that begs the question, was the heap in C++ and/or Smalltalk so named for the above queried reason?
>
2. If so, would it be correct that there would be a heap per standard block size?Not sure what you are referring to but probably a detail of the implementation. And since there are different levels the question doesn't mean much.
However OS allocations are always by block if that helps. After that it requires making the question much, much more specific.
3. Also, at what level of granularity would a heap typically be used (memory page, memory blocks, individual words (4-bytes))?Again not specific enough. A typical standard implementation of heap could not be at the word level. And it is unlikely, but not impossible, that variations would support word size allocations.
The VM heap might use word boundaries (but not size), where the application heap certainly does (word boundary.)My understanding of it is that the application would request blocks from the OS, and then something like malloc would manage the memory within the allocated blocks. malloc (or whatever equivalent Java uses) would have to keep track of the memory it has allocated somehow, and I would think it would have to do this at the word level, since it's most commonly going to allocate memory at the word level to be references to other objects, etc.
So I guess my question here would really be, if the dynamic memory heap is so named because there has been a memory management strategy that relied upon a heap data structure (which I've found no proof, but have found some suggestive literature), then would that probably have applied at the OS Page Fault level, tracking allocated blocks, or would that have applied at the malloc level, allocating individual words as necessary?
>
4. What would be the most likely property one would use as a key. That is, what makes the root item on the heap ideal?"Key" is not a term that will apply in this discussion.
You appear to be referring to strategies for effective allocation of memory such as allocations from different regions by size comparison.
It is possible that all levels might use such an allocator. General purpose applications do not sort allocations though (as per your one reference that mentions 'key'.) Sorry, I got the term "key" from an article I read regarding heaps, that indicates that a "key" is used to sort the elements, which I guess would be a more generalized way to make a heap than assuming a natural ordering on the elements in the heap. I'm not sure if the terminology is standard.
>
5. Would a industrial strength system like the jvm use a (perhaps modified or tuned) heap for this sort of task, or would this typically be too naive for an real world solution today?Again too indefinite. The Sun VM uses a rather complicated allocator, the model for which originated after years of proceeding research certainly in Smalltalk and in Lisp as well, both commercially and academically.
I am sure the default is rules driven either explicitly or implicitly as well. So it is self tuning.
There are command line options that allow you to change how it works as well.I guess perhaps I could attempt to clarify my initial question a bit.
There is a 1:1 correspondence between the runtime stack, and a stack data structure. That is, when you call a function, it pushes a stack frame onto the runtime stack. When you return from a function, it pops a stack frame from the runtime stack. This is almost certainly the reasons the runtime stack is named as it is.
The question is, is there or has there ever been a 1:1 correspondence between some aspect of the dynamic memory heap or how it is managed, and a heap data structure? If so, it would explain the name, but I'm a bit puzzled as to how a heap data structure would be of assistance in creating or managing the dynamic memory heap. If not, on the other hand, then does anybody know where the name "heap" came from, as it applies to the dynamic memory pool?
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Thnaks
Sat

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I have Done All the Back end Settings For Roster.However when i am trying to Create relationship between Roster and an Org unit,there is no avaibility Of Rosters.Can Someone Please Guide me Out.
Thanks,
Punam

HI,
There are standard relationship for Rosters (91 ,92 ,93 and 94),
but befor doing all the configuration you have to activate switch for roster
Go to transaction SHDG
Choose the path Application Components-> payroll->India->India public sector.
Click on change Global fields Icon and add the value as u2018Xu2019 for data element u201CPIN_SW_INPSu201D.
Activate the entry
Warm Regards,
Kapil Kaushal

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Jeff Henke

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Hi,
I have to calculate working days between two date fields excluding the weekends and public holidays for Switzerland.
I have written the routine using factory calender and its working fine except for two problems now:
1. If any one of the date field is empty then teh rsult should be zero.
2. And the below code is working from 1996 but my cleints wants it to work for years before 1996 as well.
I also tried to change the Start date in SCAL for factory calendar but it says enter values between 1995 to 2020.
I am new to ABAP. Please help me how i can achieve these for below code.
DATA: IT_HOLIDAYS type TABLE OF ISCAL_DAY,
      IS_HOLIDAYS TYPE ISCAL_DAY.
DATA: T_DATE TYPE SY-DATUM,
      P_DATE TYPE SY-DATUM.
DATA : X_DATE(4) TYPE C.
DATA: CNT TYPE I.
REFRESH : IT_HOLIDAYS.
CLEAR : IT_HOLIDAYS.
T_DATE = SOURCE_FIELDS-/BIC/ZCCCHP812.
P_DATE = SOURCE_FIELDS-/BIC/ZCCCHP810.
CALL FUNCTION 'HOLIDAY_GET'
EXPORTING
HOLIDAY_CALENDAR = 'CH'
FACTORY_CALENDAR = 'CH'
DATE_FROM = P_DATE
DATE_TO   = T_DATE
TABLES
HOLIDAYS = IT_HOLIDAYS
EXCEPTIONS
FACTORY_CALENDAR_NOT_FOUND = 1
HOLIDAY_CALENDAR_NOT_FOUND = 2
DATE_HAS_INVALID_FORMAT = 3
DATE_INCONSISTENCY = 4
OTHERS = 5.
DESCRIBE TABLE IT_HOLIDAYS LINES CNT.
X_DATE = T_DATE - P_DATE - CNT.
RESULT = X_DATE.
Please help
Regards
Zabina
Edited by: Syed786 on Nov 2, 2011 9:15 AM

Hi Zabina,
Try this function module 'DURATION_DETERMINE'.
Give the factory calendar and unit as DAY
With regards,
Rajesh

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