RE: high temp space usage for same analytic function on latest version
Date: Thu, 17 Nov 2022 14:48:14 -0500
Message-ID: <21b701d8fabd$8a8f26f0$9fad74d0$_at_rsiz.com>
storage indexes are like Bloom filters on steroids. If unneeded data is tossed into anything to be filtered by predicates, then depending on when it is filtered it can dramatically increase the “n” in a lot of n log n operations, and if a correctly working storage index prunes the data blocks returned dramatically, then a lot of data doesn’t need any temp space. If your data is well clustered (rows per block) with respect to predicates, this can be an amazing reduction in the blocks handled in the compute engine at all.
It probably has nothing to do with already filtered data being operated on by an analytical function.
BTW, which analytical function?
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of yudhi s
Sent: Thursday, November 17, 2022 12:45 PM
To: Mark W. Farnham
Thank you Mark. Actually the issue we are having is suddenly post migration to oracle 19.15 from 19.11 the temp space consumption for evaluating an analytical function has been increased( it's going beyond ~3 terabyte+) for similar volume of input data and it's making the query to fail with insufficient temp space error. We are trying to see if any possible way the temp spill can be minimized. And also I can't think of, how a missing storage index would play a role here.
On Thu, 17 Nov, 2022, 5:55 pm Mark W. Farnham, <mwf_at_rsiz.com> wrote:
Without looking at much of the thread, is it possible that you have storage indexes that have become invalid?
Other than a side effect of delivering pant loads of data to the compute engine for filtering there when they might being valid have slenderized data retrieval significantly, my recollection is that no complaint will be in the traces. This could be completely off target and may not be related to your case at all, but it should not take much effort to look.
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of yudhi s
Sent: Wednesday, November 16, 2022 1:44 PM
To: Lok P
Yes I tried that and it does increase the estimates for the cte from 38k to 860k but that problematic section of the plan remains same consuming terabytes of temp space.
On Thu, 17 Nov, 2022, 12:10 am Lok P, <loknath.73_at_gmail.com> wrote:
Did you try forcing the opt_estimate hint to influence the cte estimation to increase 18 times as Jonathan suggested? Does that change anything in the execution path?
On Wed, 16 Nov, 2022, 11:24 pm yudhi s, <learnerdatabase99_at_gmail.com> wrote:
Extremely sorry, as it looks like I have messed it up. Trying to correct it.
Basically we had a sql profile attached in past while we were in version 11.2.0.4 and was working fine. also when we moved to 19.11 too that same profile was there making the query finish without any issue. but that same plan is now making the query to go for consuming terabytes of temp on version 19.15. I dont have a sql monitor from 19.11 plan which was succeeding fine, but its the same plan phv as the 19.15 plan which i posted below in the 2nd sql monitor.
However, the point i want to make here is , all of these plans are almost same with minor difference. And If you see the specific section of the plan which does the "HASH JOIN OUTER" and passing the resulting output to the analytical function is exactly same in all these cases but still the 19.15 version is going for ~1TB+ temp. So its definitely odd.
Below is the three comparison of that exact section of the plan which is playing key role here in consuming all tempspace. In the first case even if the ~7Billion rows in getting sorted using just ~10GB of tempspace, whereas in second and third cases its using in TBs. Though the data volume is higher but this excessive use of tempspace is not justified. Definitely seems buggy.
https://gist.github.com/databasetech0073/55c5722da8105dfcc647ab3bd1b24a48
And also as you have highlighted the bug related to bloom filter i tried forcing the (no_px_join_filter hints and even setting up "_bloom_filter_enabled" and "_bloom_pruning_enabled" in session level to stop the bloom pruning and tried running SELECT part of the query, but still its using same excessive amount of tempspace.
--1st sqlmonitor
Below is the sql monitor and outline in version 11.2.0.4, which was finishing by consuming <20GB tempspace.
https://gist.github.com/databasetech0073/630dad9fc43d6ab6c8863251e29f1cf2
--2nd sql monitor
Below is the sql monitor and outline in version 19.15 (by forcing exactly the same plan through a sql profile as it used to take in 11.2).
https://gist.github.com/databasetech0073/37ec33e73a23bd0055148ba43a0a49ca
--3rd sql monitor
Below is the sql monitor and outline in current version ( i.e 19.15 without any profile) which is also consuming high tempspace.
https://gist.github.com/databasetech0073/4b895f5790a993ed326d389b54295f9b
On Tue, 15 Nov, 2022, 6:39 pm Jonathan Lewis, <jlewisoracle_at_gmail.com> wrote:
Since I've noticed Bloom filters as an anomaly, it might be worth checking if you're patched for:
"Bug 30618406 - Huge PGA memory consumption by bloom filters (qesblfilter_seg) in px slaves in full partition-wise join"
I know this plan isn't using full PW joins - but (read the details) - your parallel operation uses a lot of memory, and then a lot of temp space. Sometimes the bug goes a lot further than the initial description.
Marked as fixed in 23.1, but I can see patches for 19.16 in the RU.
Regards
Jonathan Lewis
On Tue, 15 Nov 2022 at 07:15, Jonathan Lewis <jlewisoracle_at_gmail.com> wrote:
I've taken a few minutes to look through the github material. The headings don't agree with the contents. Here's a list showing each heading plus two lines from the Outline Data under the heading:
Display cursor plan from version 11.2.0.4
Execution which is failing in 19.15 version with high tempspace consumption
Execution which was running fine in 19.11 version
There doesn't seem to be any point in spending time looking at detail when I've got no confidence that the bits of information supplied belong together.
A couple of high visibility points, though:
76 - storage((COALESCE("FPT"."DEL_FLG",'N')='N' AND TRUNC(INTERNAL_FUNCTION("FPT"."H_DT_TIM"))=:B1 AND SYS_OP_BLOOM_FILTER(:BF0000,"FPT"."A_FK")))
filter((COALESCE("FPT"."DEL_FLG",'N')='N' AND TRUNC(INTERNAL_FUNCTION("FPT"."H_DT_TIM"))=:B1 AND SYS_OP_BLOOM_FILTER(:BF0000,"FPT"."A_FK")))
Regards
Jonathan Lewis
On Mon, 14 Nov 2022 at 17:18, yudhi s <learnerdatabase99_at_gmail.com> wrote:
Thank You Sayan and Jonathan.
As you suggested, as a quick thing , in the select query, I was trying this hint in the main block to influence optimizer to increase the resulting rows ~18 times from the CTE "C" , but its not getting reflected in the plan, which means optimizer is not considering this, but then it should appear in the hint report section of the plan as error or unused etc.. but it is not getting published there too, so not sure why is this happening. Is there anything wrong in the hint below which i am using?
I am using below hint in the main select query which performs outer join with the "cte" Table C
/*+OPT_ESTIMATE( TABLE, C, scale_rows=18)*/
Also , I tried as below but seeing no change to the tempspace consumption though.
cast(RPAD (SUBSTR (CP.CP_NBR, 1, CP.CPCL_NBR - X.RN),CASE CP.PANL_CNT WHEN 0 THEN 16 ELSE CP.PANL_CNT END, '9') as varchar2(22)) AS HIGH_VALUE
cast(RPAD (SUBSTR (CP.CP_NBR, 1, CP.CPCL_NBR - X.RN), CASE CP.PANL_CNT WHEN 0 THEN 16 ELSE CP.PANL_CNT END, '0') as varchar2(22) ) AS LOW_VALUE,
On Mon, 14 Nov, 2022, 4:22 pm Jonathan Lewis, <jlewisoracle_at_gmail.com> wrote:
Still avoiding spending a lot of time on the github text.
Regards
Jonathan Lewis
On Sun, 13 Nov 2022 at 14:28, yudhi s <learnerdatabase99_at_gmail.com> wrote:
Thank you Lok. Actually the join is not exactly on the columns but with some functions so that might be the case why it seems like Cartesian.
However the point is , this query has not been changed and I agree that it may be because the data has been increased a lil in one of the table 'C' or 'T' , so the join output has been increased from 7billion to 10billion but how come that justifies the temp space requirement from 20gb to 2.5terabyte it not twice or thrice but multiple times.
As this query is running in parallel-16 degree because of a underlying table degree , and considering no other option at hand, so I was thinking if by increasing or decreasing the parallelism with help of hints will help in completing the query at least with lesser temp space(we have 2.5TB of temp space with us right now currently) ? Or any other possible option to make this query succeed?
Just to note , we had initially 200gb of temp space but just with the hope that this query may finish, we already increased it to 2.5TB now, but still no luck and the query is failing and it's happening after this 19.15 patch.
On Sun, 13 Nov, 2022, 6:06 pm Lok P, <loknath.73_at_gmail.com> wrote:
The below section you posted shows the input to 'Hash join outer' were ~1Million and 37milion respectively, but the result came from the outer join is ~7billion. So is there any oddity in the data in table 'T' and 'C' which is playing a role which is increasing the rows input to your analytical function recently?
SQL Plan Monitoring Details (Plan Hash Value=2056239125)
On Sun, Nov 13, 2022 at 2:34 AM yudhi s <learnerdatabase99_at_gmail.com> wrote:
Thank you Jonathan.
Actually the original query was a long one so i was trying to reduce the complexity by just posting the particular section of the query which was causing the temp space spike. But I agree that just a partial query doesn't make much sense. Also my apology as the plan format was distorted.
I have again posted the exact query below with the actual object names being replaced with dummy names. I have posted the plan in the github in the link below, so the sql execution plan format will be intact. And I am not having the "display cursor" plan for the current runs/failures for this INSERT query, so i have posted the sql monitors for them and i had the display cursor plan when it was running fine in 11.2.0.4 so i posted that just for reference. Also I have copied and pasted the outline section from the display_awr below each of the sqlmonitor plan.
https://gist.github.com/databasetech0073/714263bce477f624763f757e457cb861
As mentioned earlier, the section of the plan which is doing the outer join is below and it results in ~10billion rows. Which then is passed to the analytical function. Was trying to understand, Is there any possible way to minimize the temp space consumption in this scenario? because we kept on increasing the temp space assuming it would succeed somehow, but it just kept consuming 2.5TB+ space and then also it failed with "Ora-01652 unable to extend temp segment .." as it saturates all allocated temp space?
As far as I know the encryption/TDE was already there in this database before we moved from 19.11 to 19.15. I will double check with the infra team on this.
"LEFT OUTER JOIN C
On Sat, Nov 12, 2022 at 12:50 PM Jonathan Lewis <jlewisoracle_at_gmail.com> wrote:
>> We reran the query and it took a different plan hash value , however the path is almost similar wrt the line which does "Outer join" and the "analytical function" evaluation. I have posted the specific section of sql monitor below with predicate and column projection for that run.
The supplied outputs are virtually unreadable, for different execution plans, for different versions (and youve changed from 19.11 for the "slow" query to 11.2.0.4!) , and partial. I'm not going to look at them.
>> However, the sql monitor shows status as 'error' out after sometime(~30minutes)) but the underlying sessions(~33 parallel sessions) kept on running for 2hrs+
That looks like the behaviour that Mohamed Houri has written about in the past: https://hourim.wordpress.com/2020/03/07/sql-monitor-flaw/
I'd forgotten it would be harder to collect the correct statistics from all the processes when running a parallel query - finding sessions by SQL_ID could work, but using views like v$px_sesstat etc. is safer. Nothing stands out from the information you supplied about wait events, and the only "unusual" thing in the session activity is that you are writing encrypted blocks to the temporary tablespace - were you doing that in the earlier version? It shouldn't explain a massive increase in space requirements, but it might be relevant - it would help to explain an increase in CPU.
Regards
Jonathan Lewis
On Fri, 11 Nov 2022 at 17:07, yudhi s <learnerdatabase99_at_gmail.com> wrote:
Thank You Sayan, Jonathan.
We reran the query and it took a different plan hash value , however the path is almost similar wrt the line which does "Outer join" and the "analytical function" evaluation. I have posted the specific section of sql monitor below with predicate and column projection for that run. However, the sql monitor shows status as 'error' out after sometime(~30minutes)) but the underlying sessions(~33 parallel sessions) kept on running for 2hrs+, until then I saw ~2TB of temp space already consumed and later it failed with insufficient temp space error.
Cc: Lok P; Jonathan Lewis; Oracle L
Subject: Re: high temp space usage for same analytic function on latest version
Cc: Jonathan Lewis; Oracle L
Subject: Re: high temp space usage for same analytic function on latest version
OPTIMIZER_FEATURES_ENABLE('19.1.0')
DB_VERSION('19.1.0')
OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
DB_VERSION('19.1.0')
OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
DB_VERSION('11.2.0.4')
| Id | Operation | Name | Rows | Cost | Time | Start | Execs | Rows | Read | Read | Write | Write | Cell | Mem | Temp | Activity | Activity Detail |
| | | | (Estim) | | Active(s) | Active | | (Actual) | Reqs | Bytes | Reqs | Bytes | Offload | (Max) | (Max) | (%) | (# samples) |
| | | | | | | | | | | | | | | | | direct path read temp (553) |
| | | | | | | | | | | | | | | | | | direct path write temp (47) |
| 31 | HASH JOIN RIGHT OUTER | | 9M | 2M | 1676 | +218 | 16 | 7G | | | | | | 217M | | 23.08 | Cpu (4041) |
| 32 | BUFFER SORT | | | | 4 | +216 | 16 | 1M | | | | | | 97M | | | |
| 33 | PX RECEIVE | | 10647 | 24 | 4 | +216 | 16 | 1M | | | | | | | | | |
| 34 | PX SEND HASH | :TQ10005 | 10647 | 24 | 1633 | +216 | 1 | 1M | | | | | | | | 0.01 | Cpu (2) |
| 35 | VIEW | | 10647 | 24 | 1632 | +217 | 1 | 1M | | | | | | | | | |
| 36 | TABLE ACCESS STORAGE FULL | SYS_TEMP_0FDA1E71E_D71F1BDE | 10647 | 24 | 1632 | +217 | 1 | 1M | 106 | 104MB | | | | | | 0.01 | cell multiblock physical read (1) |
| 37 | PX RECEIVE | | 9M | 2M | 1676 | +218 | 16 | 37M | | | | | | | | 0.05 | Cpu (9) |
| 38 | PX SEND HASH | :TQ10009 | 9M | 2M | 1677 | +217 | 16 | 37M | | | | | | | | 0.13 | Cpu (23) |
| 39 | VIEW | | 9M | 2M | 1677 | +217 | 16 | 37M | | | | | | | | | |
ON SUBSTR (T.C_NBR, 1, 4) = C.BNK_ID_NB_4
AND LENGTH (T.C_NBR) = C.PANL_CNT
AND T.C_NBR BETWEEN C.LOW_VALUE AND C.HIGH_VALUE) S"
--
http://www.freelists.org/webpage/oracle-l
Received on Thu Nov 17 2022 - 20:48:14 CET