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| Re: pctfree and pct used [message #103027 is a reply to message #102994] |
Fri, 17 January 2003 00:51   |
Maithily
Messages: 5
Registered: December 2002
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Junior Member |
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Hi,
PCTFREE and PCTUSED are the block storage parameters.
1. PCTFREE- This parameter is used to specify how much space should be left in the block for updates.
For eg. if The PctFree for a block is 30, then Oracle keeps on adding new rows to the block until the block is 70 % full. It leaves the 30 % for future updates. That is, in case, any row is updated and requires some more space, it is taken out from the 30 % remaining in the Block. U should specify the Value of this parameter HIGH if future updates in the rows of the table are going to need more space. In case ur table is less prone to updates, then this value can be specified LOW.
PCTUSED : As I have mentioned above, Oracle stops INSERTING new Rows in a table when the space usage reaches the PCTFREE limit.
Now consider this ---- When should Oracle start inserting new rows in the Block ?
PctUSED parameter is taken into consideration for the answer of the above question.
Suppose u have specified PCTUSED as 40 %. and PCTFREE as 20 %.
1. Oracle will keep on inserting new rows till the space is 80 % used. It will reserve the remaining 20% for future updates.
2. To start adding new rows again to the block, Oracle will check the space in the Block and the PCTUSED parameter.
3. When the space falls below 40 %, Oracle will start adding new rows to the block.
Hope I have explained the concept fairly.
Thanks and Regards,
Maithily
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| Re: pctfree and pct used [message #103784 is a reply to message #102994] |
Sat, 13 March 2004 20:39 |
sahadevan
Messages: 2
Registered: November 2003
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Junior Member |
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Hi,
PCTFREE and PCTUSED are the block storage parameters.
1. PCTFREE- This parameter is used to specify how much space should be left in the block for updates.
For eg. if The PctFree for a block is 30, then Oracle keeps on adding new rows to the block until the block is 70 % full. It leaves the 30 % for future updates. That is, in case, any row is updated and requires some more space, it is taken out from the 30 % remaining in the Block. U should specify the Value of this parameter HIGH if future updates in the rows of the table are going to need more space. In case ur table is less prone to updates, then this value can be specified LOW.
PCTUSED : As I have mentioned above, Oracle stops INSERTING new Rows in a table when the space usage reaches the PCTFREE limit.
Now consider this ---- When should Oracle start inserting new rows in the Block ?
PctUSED parameter is taken into consideration for the answer of the above question.
Suppose u have specified PCTUSED as 40 %. and PCTFREE as 20 %.
1. Oracle will keep on inserting new rows till the space is 80 % used. It will reserve the remaining 20% for future updates.
2. To start adding new rows again to the block, Oracle will check the space in the Block and the PCTUSED parameter.
3. When the space falls below 40 %, Oracle will start adding new rows to the block.
Hope I have explained the concept fairly.
Thanks and Regards,
Sahadevan,.M.K,
sobha Renaissance
Bangalore
India
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| Re: pctfree and pct used [message #239185 is a reply to message #102994] |
Mon, 21 May 2007 12:44 |
mivey4
Messages: 19
Registered: March 2007
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Junior Member |
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Hi.
I know that this thread has been untouched for quite a while now but I still have a question that remains unclear for which this thread addresses. So rather than open a new thread for the same question, I figured I'd just use this existing thread to post my question.
If I am wrong for doing this, please tell me and I'll open another thread.
I understand very clear how PCTFREE works but I am still a bit confused for how PCTUSED works.
So using the existing example:
PCTFREE - 20
PCTUSED - 40
The data block will continue to fill with rows of data until the PCTFREE is reached which would be 80% full.
But, if the block can't be used again until the free space falls below 40%....what is going to cause the block to decrease in size below that 40% threshold??? Delete operations?
Forgive me if this sounds like a stupid question but I can't find an explicit answer anywhere. The definitions I've seen seem to be with the presumption that the reader knows what the answer is and I just want solid clarification.
Thanks
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| Re: pctfree and pct used [message #239200 is a reply to message #239195] |
Mon, 21 May 2007 13:36 |
mivey4
Messages: 19
Registered: March 2007
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Junior Member |
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Thanks Michel -
Your explanation provided the additional clarification that I was looking for.
As for the row migration; that and the row chaining concepts I have a thorough understanding of so that "other story" is clear to me.
Thanks again!!
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| Re: pctfree and pct used [message #362280 is a reply to message #362276] |
Mon, 01 December 2008 12:26 |
ykozhevnikov
Messages: 59
Registered: November 2008
Location: USA
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Member |
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select * from dba_tables where owner='SATURN1'
I just found for some tables PCTUSED value is null,It could be server uses some default values for PCTUSED.
And dba_tables view. Field PCT_USED allowed to put null value.
ALTER table dept PCTFREE 30 PCTUSED 70 this statement does not allowed to put null. But how come null value apears in
dba_tables
Thanks Michel
[Updated on: Mon, 01 December 2008 12:43] Report message to a moderator |
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