Exadata: ORA-00600 :[25027] On Update Over Compressed Table (EHCC)

Asset ID:	1-72-1502577.1
Update Date:	2014-02-07
Keywords:

Solution Type Problem Resolution Sure

Solution 1502577.1 : Exadata: ORA-00600 :[25027] On Update Over Compressed Table (EHCC)

Applies to:

Oracle Database - Enterprise Edition - Version 11.2.0.3 and later
Exadata Database Machine V2 - Version All Versions and later
Oracle Exadata Storage Server Software - Version 11.2.3.1.0 and later
Exadata Database Machine X2-2 Hardware - Version All Versions and later
Exadata Database Machine X2-8 - Version All Versions and later
Information in this document applies to any platform.

Symptoms

Error ora-600 [25027] could be intermittently generated during update on a compressed table (using EHCC)

Cause

Updates are being executed over a compressed table. In this case, compression was EHCC ENABLED for QUERY HIGH. The issue is observed when row to be updated is stored on an uncompressed block. For example, following block dump comes from the generated trace file.

In this example, Oracle is trying to update row 103 in block 0x2381a21d:

Block header dump: 0x2381a21d
Object id on Block? Y
seg/obj: 0x15f8a csc: 0x9b9.7cc583d0 itc: 2 flg: E typ: 1 - DATA
brn: 0 bdba: 0x2381a200 ver: 0x01 opc: 0
inc: 0 exflg: 0

Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x013f.00e.005b3d8b 0x00eda100.6fb8.17 C--- 0 scn 0x09b9.7cc583c7
0x02 0x0176.007.001b6d41 0x00cb9aeb.340b.1a ---- 1 fsc 0x0000.00000000
bdba: 0x2381a21d

tab 0, row 103, @0x5cfe
tl: 82 fb: --H-FL-- lb: 0x2 cc: 12
col 0: [23] column data removed ...
col 1: [ 3] column data removed ...
col 2: [ 5] column data removed ...
col 3: [ 2] column data removed ...
col 4: [ 3] column data removed ...
col 5: [ 1] column data removed ...
col 6: [ 7] column data removed ...
col 7: *NULL*
col 8: *NULL*
col 9: [ 8] column data removed ...
col 10: [ 8] column data removed ...
col 11: [ 7] column data removed ...
tab 0, row 104, @0x5ca3

Itl 0x02 shows that row was been locked and row header shows flag fb: --H-FL--, which means row is completely stored on this block (it has head, first, and last piece bits set).

Although row has been locked, it seems Oracle tries to read a block with the next row piece and error is reported as block does not exist.

Previous example shows and uncompressed block. But also problem could reproduce while updating an oltp compressed block. This is, problem could reproduce updating a no-ehcc compressed block on an EHCC object.

Following is an example of what you may found in a EHCC compressed data block dump, so you can compare it with an uncompressed or oltp compressed data block dump.

tosp=0x325e
   r0_9ir2=0x0
   mec_kdbh9ir2=0x0
                  76543210
   shcf_kdbh9ir2=----------
              76543210
   flag_9ir2=--R-----   Archive compression: Y       -----> Compression flags
       fcls_9ir2[0]={ }
0x16:pti[0]   nrow=2   offs=0
0x1a:pri[0]   offs=0x327a
0x1c:pri[1]   sfll=0
block_row_dump:
tab 0, row 0, @0x327a
tl: 3334 fb: -----LP- lb: 0x0 cc: 1
col 0: [3328]
Compression level: 01 (Query Low)         -----> EHCC Type of compression

Solution

Problem is caused by bug:14138130. Solution is to apply the fix for this bug.

Possible workaround:

- Uncompress the table

References

<NOTE:560103.1> - Ora-600 [25027] While Inserting Into a Table

Attachments

This solution has no attachment