What cause the big diffrence on the same sql ?

1.DELETE FROM PUB_QUEUE
WHERE
 ROWID = :B1


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        0      0.00       0.00          0          0          0           0
Execute    261      0.00       0.18          0        261       1093         261
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total      261      0.00       0.18          0        261       1093         261

Misses in library cache during parse: 0
Optimizer mode: CHOOSE
Parsing user id: 29  (LSS)   (recursive depth: 1)

Rows     Execution Plan
-------  ---------------------------------------------------
      0  DELETE STATEMENT   MODE: CHOOSE
      0   DELETE OF 'PUB_QUEUE'
      0    TABLE ACCESS (BY USER ROWID) OF 'PUB_QUEUE' (TABLE)
               PARTITION:ROW LOCATION




2.DELETE FROM PUB_QUEUE
WHERE
 ROWID = :B1


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        0      0.00       0.00          0          0          0           0
Execute    511    253.46     248.94          2    6625899       3932         511
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total      511    253.46     248.94          2    6625899       3932         511

Misses in library cache during parse: 0
Optimizer mode: CHOOSE
Parsing user id: 37  (LSS)   (recursive depth: 1)

Rows     Execution Plan
-------  ---------------------------------------------------
      0  DELETE STATEMENT   MODE: CHOOSE
      0   DELETE OF 'PUB_QUEUE'
      0    TABLE ACCESS   MODE: ANALYZED (BY USER ROWID) OF 'PUB_QUEUE'
               (TABLE) PARTITION:ROW LOCATION

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