IDS Forum

count/insert vs insert

Posted By: Cesar Inacio Martins
Date: Wednesday, 21 September 2011, at 4:49 p.m.

Hi,

I already see here some recommendations when execute an insert , if
should check before or not if the record exists or if better check if
occur some constraint error (unique index/PK).

As far I remember , the better way on most of the cases, is try insert
and than check if was occur successfully.
I executed a few tests and have 3 doubts. Please follow the tests bellow.
(ifx 11.50 fc8 aix , 4gl 7.32)

After write a little code using 4GL and executing 5 times :
1) execute just an insert for a record what don't exists on the table.
(the insert occur successful)

sesid 7396
2) execute a "select first 1 1 from table" + if sqlca.sqlcode =
notfound, than execute the insert (the insert occur successful because
the record don't exists)

sesid 7409
3) execute just an insert for a record where the unique key (not PK)
already exists (the program abend with error -239)

sesid 7412
4) execute a "select first 1 1 from table" + if sqlca.sqlcode =
notfound, so the insert wasn't executed because the record already exists

sesid 7421
5) execute just an insert for a record where the PK already exists (the
program abend with error -268)

sesid 7470

(I add a PK over the UK)

The result what I got appear to confirm, using just the insert is better
and check later if occur some error.
And appear be better if use PK instead only UK.
This outputs I gather from sys* , saving at sysdbclose...

sesid lockreqs lockwts logrecs maxlog_kb isreads iswrites isrewrites
isdeletes iscommits seqscans total_sorts cpu_time
7396 928 0 6 0.56 664 51 0 0 1 3 0
0.73029
7409 867 0 6 0.56 636 51 0 0 1 3 0
0.95809
7412 854 0 8 0.61 644 52 0 0 0 3 0
0.61418
7421 888 0 0 0.00 660 51 0 0 0 3 0
0.8001
7470 1042 0 10 0.74 718 50 0 0 0 3 0
0.07048

The fields what I pay attention: logrecs, maxlog_kb, iscommits, cpu_time

sesid logrecs maxlog_kb iscommits cpu_time
7396 6 0.56 1 0.73029
7409 6 0.56 1 0.95809
7412 8 0.61 0 0.61418
7421 0 0.00 0 0.8001
7470 10 0.74 0 0.07048

What caught my attention is the use of logical log records and the
little cpu_time when the table have a PK instead only the UK.

My Doubts
1)On the session 7412 , where run the insert and check for errors
after(UK violated). I strange the grown of logical log record.
Checking the logs (with onlog) I see the engine adding the 2 others
index (ADDITEM) before add the UK index and then abend with error.
Should be better the engine always insert first the UK constraints , to
avoid the ADDITEM and the rollback of each one if occur a violation on
the constraint?

2) On this situation (sesid 7412), where the CPU consumption is instead
check before if the record exists (sesid 7421) and having more logical
log records... this way still better way to work ? considering the using
of logical log x cpu_time (looking at this isolate context, test-by-test)

3) On sesid 7470, where I add a PK to table, the engine appear have the
same behave of UK , adding each index of the table before the UK/PK
(onlog/ADDITEM) and then abending with -268 error. How could be the
engine consume 10 times less CPU of the database!???

Cesar

Messages In This Thread

• count/insert vs insert
  Cesar Inacio Martins -- Wednesday, 21 September 2011, at 4:49 p.m.
  • Re: count/insert vs insert
    Art Kagel -- Wednesday, 21 September 2011, at 6:49 p.m.
    • Re: count/insert vs insert
      John Miller iii -- Wednesday, 21 September 2011, at 7:19 p.m.
      • Re: count/insert vs insert
        Cesar Inacio Martins -- Thursday, 22 September 2011, at 7:15 a.m.
        • Re: count/insert vs insert
          Art Kagel -- Thursday, 22 September 2011, at 8:37 a.m.

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