Oracle get UNIQUE constraint violation error too late - sql

Question

What should I check why Oracle server takes more then 20 sec to return UNIQUE constraint violation error for specific data?
One of our processes is processing over 30000 data one day with multi process and some time gets UNIQUE constraint violation error in 1 sec
but it takes more then 20 sec to return UNIQUE constraint violation error for specific data.
Query is same as below. (Modified only table name)
MERGE
INTO TableA S
USING (
SELECT NVL(:sccm_cd , ' ') SCCM_CD
, NVL(:oder_dt , ' ') ODER_DT
, NVL(:mrkt_dstn_cd, ' ') MRKT_DSTN_CD
, NVL(:oder_no , ' ') ODER_NO
, NVL(:cncd_unpr , 0) CNCD_UNPR
, B.SLBY_FEE_GRD_CD
, B.ACCT_MNGR_EMPL_NO
, C.AO_FEE_GRD_CD
FROM DUAL A
, TableB B
, TableC C
WHERE 1 = 1
AND B.SCCM_CD = :sccm_cd
AND B.ACNO = :acno
AND C.SCCM_CD(+) = B.SCCM_CD
AND C.EMPL_NO(+) = B.ACCT_MNGR_EMPL_NO
) T
ON ( S.sccm_cd = T.sccm_cd
AND S.oder_dt = T.oder_dt
AND S.mrkt_dstn_cd = T.mrkt_dstn_cd
AND S.oder_no = T.oder_no
AND S.cncd_unpr = T.cncd_unpr
)
WHEN MATCHED THEN
UPDATE
SET S.cncd_qty = S.cncd_qty + NVL(:cncd_qty ,0)
, S.slby_fee = S.slby_fee + NVL(:slby_fee ,0)
, S.slby_fee_srtx = S.slby_fee_srtx + NVL(:slby_fee_srtx,0)
, S.idx_fee_amt = S.idx_fee_amt + NVL(:idx_fee_amt ,0)
, S.cltr_fee = S.cltr_fee + NVL(:cltr_fee ,0)
, S.trtx = S.trtx + NVL(:trtx ,0)
, S.otc_fee = S.otc_fee + NVL(:otc_fee ,0)
, S.wht_fee = S.wht_fee + NVL(:wht_fee ,0)
WHEN NOT MATCHED THEN
INSERT (
sccm_cd
, oder_dt
, mrkt_dstn_cd
, oder_no
, cncd_unpr
, acno
, item_cd
, slby_dstn_cd
, md_dstn_cd
, cncd_qty
, stlm_dt
, trtx_txtn_dstn_cd
, proc_cmpl_dstn_cd
, item_dstn_cd
, slby_fee_grd_cd
, slby_fee
, slby_fee_srtx
, idx_fee_amt
, cltr_fee
, trtx
, wht_fee
, otc_fee
, acct_mngr_empl_no
, ao_fee_grd_cd
)
VALUES
( T.sccm_cd
, T.oder_dt
, T.mrkt_dstn_cd
, T.oder_no
, T.cncd_unpr
, :acno
, :item_cd
, :slby_dstn_cd
, :md_dstn_cd
, NVL(:cncd_qty ,0)
, DECODE(:mrkt_dstn_cd, 'TN', T.oder_dt, :stlm_dt)
, :trtx_txtn_dstn_cd
, '0'
, :item_dstn_cd
, NVL(:slby_fee_grd_cd, T.SLBY_FEE_GRD_CD)
, NVL(:slby_fee ,0)
, NVL(:slby_fee_srtx ,0)
, NVL(:idx_fee_amt ,0)
, NVL(:cltr_fee ,0)
, NVL(:trtx ,0)
, NVL(:wht_fee , 0)
, NVL(:otc_fee , 0)
, T.acct_mngr_empl_no
, T.ao_fee_grd_cd
)

Answer 1

There could be multiple reasons for it. I will list here some of the possible causes for this behavior.
Concurrency issue
Your insert might be waiting for other operations, like other inserts or updated or deletions.
Network issues
It is possible that for some reason your network is overwhelmed with requests or, if the server is remote, this could be an internet speed issue as well.
Server load
The server might be overwhelmed with lots of jobs to do.
Slow query
It's also possible that the select you use in your insert command is very slow. It would make sense to test its speed. Also, it would make sense to test insert speed as well.