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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Enqueue TX level 4 wait -- blocks dump
Hi Jonathan.
Thanks for answering.
> Do you mean that the value from ini_trans in
> dba_tables and dba_indexes were 10 and 11
> respectively ?
Exactly.
> If so, then you should expect the number of
> ITL slots in the tables and indexes to be 10
> and 11 (assuming the initrans was not altered
> on the fly after data had been entered). If
> you want to determine the actual concurrency
> from the block dumps, you would have to guess,
> based on how close the SCNs were in the ITL
> entries.
Let me tell you what I tried to do.
For indexes for example, in many blocks all the ITLs had been used,
wouldn't that mean that at some point in time there were 11 simultaneous
transactions active? (counting also the recursive ones)
Index example.
Block header dump: 0x55802364
Object id on Block? Y
seg/obj: 0xb456 csc: 0x00.d86ff6c itc: 11 flg: - typ: 2 - INDEX
fsl: 0 fnx: 0x0 ver: 0x01
Itl Xid Uba Flag Lck Scn/Fsc0x01 xid: 0x0002.012.00019480 uba: 0x10c0170e.240b.02 C--- 0 scn 0x00
Leaf block dump
By checking the ITC value I was trying to find an ITC higher than 11, if I was lucky and found something like that, this would have meant that at some point in time there were more than 11 transactions going on and that an additional ITL slot was needed and was allocated (as maxtrans and pctfree allowed it). am I correct?
I really appreciate your comments.
Thank you.
Regards,
Diego.
>
> Can you clarify your comments about ITL and ITC.
>
> Do you mean that the value from ini_trans in
> dba_tables and dba_indexes were 10 and 11
> respectively ?
>
> If so, then you should expect the number of
> ITL slots in the tables and indexes to be 10
> and 11 (assuming the initrans was not altered
> on the fly after data had been entered). If
> you want to determine the actual concurrency
> from the block dumps, you would have to guess,
> based on how close the SCNs were in the ITL
> entries.
>
> TX/4 arises from many causes - the most likely
> one on inserts into heap tables relates to collision
> on primary keys and foreign keys.
>
> Could you have multiple processes trying to
> insert the same PK, waiting, failing, then using
> the next value from a sequence number to try
> again ? Could you have processes inserting
> child rows for parent rows that had not yet
> been created ... and so on.
>
>
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> The Co-operative Oracle Users' FAQ
> http://www.jlcomp.demon.co.uk/faq/ind_faq.html
>
> Optimising Oracle Seminar
> http://www.jlcomp.demon.co.uk/seminar.html
>
> June 2004 UK Manchester
> July 2004 Iceland
> July 2004 USA California
> Aug 2004 USA North Carolina
> Sept 2004 UK Manchester
> Sept 2004 USA NYC
> Oct 2004 USA Boston
>
>
> ----- Original Message -----
> From: "Diego Cutrone" <diegocutrone_at_yahoo.com.ar>
> To: "Oracle List" <oracle-l_at_freelists.org>
> Sent: Monday, May 03, 2004 9:35 PM
> Subject: Enqueue TX level 4 wait -- blocks dump
>
>
> Hi everybody,
> I have a question on TX enqueues.
> I'm seeing a lot of TX enqueues level 4 on a table. I have also found that
> the statement that was waiting on this wait was an ***INSERT*** operation.
>
> Oracle 8i
> Table:
> ITL = 10
> 4 FREELISTS
> 4 FREELISTS GROUPS
> PCTFREE 20
>
> I dumped every table block and checked the ITC entry. I found ITC was
almost
> always 10 for every block.
> Then I checked for the average free space within the blocks, (supposing
the
> block had needed an additional ITL slot) and again I found that in every
> block there was at least 80 bytes free. (as Avsp reported).
>
> So I went for the indexes
>
> ITL = 11
> 4 FREELISTS
> 4 FREELISTS GROUPS
> PCTFREE 10
>
> and I found no problem at all in the ITC entries.(most of them were 11)
> But I found many blocks with kdxcoavs = 0. (no free space on them).
>
> Taking into consideration that we're talking about an INSERT,
> Can it be possible that the TX 4 is being caused by an ITL shortage in the
> index?
>
> (All slots are being used and there's no free space in the block, so when
a
> new INSERT needs to put its entry in that block, despite of the fact that
> this block will surely need to split because there's no free space left in
> it, the transaction first needs to get a free ITL slot and as they are all
> taken and there's no free space it has to wait in a enqueue TX 4. Is this
> the way it works on this case?)
>
> What do you think?
>
> Thanks,
> Diego.
>
>
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