Re: Insert Query issue

Thank you Lothar.

It appears to be something matching to delayed block cleanout effect in which post DML sometimes we have to perform a segment scan so that the commit scn can be updated for all the blocks and for that sometimes we have to do it using manual stats gathering or forced segment full scan to pass all the data blocks through buffer cache. But for that we used to see one stats i.e. 'transaction table consistent read undo records applied' on the SELECT query execution.

So is this tidying up of block post delete something similar as above and we can get that verified and confirmed from some session statistics from v$sesstat while the insert is running at run time? Also I am thinking what can be done so as to tidying up the blocks after delete, if a force segment full scan or stats gather post deletion can anyway help, so as to not impact the insert performance?

> Betreff: Re: Insert Query issue
> Datum: Thu, 29 Jul 2021 19:59:25 +0200
> Von: Lothar Flatz <l.flatz_at_bluewin.ch> <l.flatz_at_bluewin.ch>
> An: oracle-l_at_freelists.org
>
> Hi,
>
> there reason should be that after a delete rows are marked as technical
> deleted, but the block is not yet tidied up. (I suppose that would mean
> e.g. that other rows are not yet shifted for contiguous space etc.)
> The tidying is done on the next insert, which therefore will be
> substantially slower for once.
> I heard this explanation long ago , but suppose it still holds.
> My whole understanding of this is a bit vague.
> I guess Jonathan could fill in some details here.
>
> Regards
>
> Lothar
>
> Am 29.07.2021 um 18:10 schrieb Pap:
>
> This legacy database is on version 11.2.0.4 of oracle Exadata.
>
> We are having below conventional insert query introduced and its a bulk
> insert happening with an arraysize of ~352 from informatica. And the
> response time was ~3millisec/execution i.e. for one chunk or ~352 rows. But
> we noticed suddenly the response time becomes
> tripled(~8-9millisec/execution) for the same set of rows/array size insert.
> No changes done to the underlying table structure.
>
> During digging into the AWR views we found that the increase in response
> time for this insert query started after we introduced the delete script to
> purge data from this table. The delete is also happening in bulk fashion
> with an arraysize of 100K through plsql procedure and its deleting data
> with CRE_TS<sysdate-3. And it's clear from dba_hist_sqlstat that it's the
> cpu_time_delta and IOWAIT_DELTA which increased thus making the
> ELAPSED_TIME_delta go up by three times for the INSERT query. No such
> increase in BUFFER_GETS_delta observed. But one thing we notice is that the
> DELETE is not running at exactly the same time as the insert/data load
> script runs. So howcome this delete is impacting the INSERT query? Is this
> that as delete is making some blocks empty so that now the INSERT has to
> now see through all to find the empty blocks before insert and thus
> spending more time?
>
> The table is ~215GB in size and is not partitioned holding ~1.7billion
> rows. There exists only a primary key composite index on two number data
> type columns. With Blevel-3 , and having index size ~65GB with ~7.3million
> leaf blocks.
>
>
> Below is the AWR plan for the INSERT and DELETE queries.
>
> INSERT INTO TAB1(TAID,TID,AID,APP_NM,CRE_TS) VALUES ( :1, :2, :3,:4, :5)
>
>
> -------------------------------------------------
> | Id | Operation | Name | Cost |
> -------------------------------------------------
> | 0 | INSERT STATEMENT | | 1 |
> | 1 | LOAD TABLE CONVENTIONAL | | |
> -------------------------------------------------
>
> Query Block Name / Object Alias (identified by operation id):
> -------------------------------------------------------------
>
> 1 - INS$1
>
> Note
> -----
> - cpu costing is off (consider enabling it)
>
>
> DELETE FROM USER1.TAB1 WHERE ROWID = :1
>
> Plan hash value: 2488984540
>
>
> ----------------------------------------------------------------------------------------------------
> | Id | Operation | Name | Rows | Bytes
> | Cost (%CPU)| Time |
>
> ----------------------------------------------------------------------------------------------------
> | 0 | DELETE STATEMENT | | | |
> 1 (100)| |
> | 1 | DELETE | TAB1 | | |
> | |
> | 2 | TABLE ACCESS BY USER ROWID| TAB1 | 1 | 25 |
> 1 (0)| 00:00:01 |
>
> ----------------------------------------------------------------------------------------------------
>
> Query Block Name / Object Alias (identified by operation id):
> -------------------------------------------------------------
>
> 1 - DEL$1
> 2 - DEL$1 / TAB1_at_DEL$1
>
> Outline Data
> -------------
>
> /*+
> BEGIN_OUTLINE_DATA
> IGNORE_OPTIM_EMBEDDED_HINTS
> OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
> DB_VERSION('11.2.0.4')
> ALL_ROWS
> OUTLINE_LEAF(_at_"DEL$1")
> ROWID(_at_"DEL$1" "TAB1"_at_"DEL$1")
> END_OUTLINE_DATA
> */
>
>
>

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