Index Compression – aargh

The problem with telling people that some feature of Oracle is a “good thing” is that some of those people will go ahead and use it; and if enough people use it some of them will discover a hitherto undiscovered defect. Almost inevitably the bug will turn out to be one of those “combinations” bugs that leaves you thinking: “Why the {insert preferred expression of disbelief here} should {feature X} have anything to do with {feature Y}”.

Here – based on index compression, as you may have guessed from the title – is one such bug. I got it first on 11.1.0.7, but it’s still there on 11.2.0.4 and 12.1.0.1

create table t1 (
	id1	number not null,
	id2	number not null,
	n1	number,
	v1	varchar2(10)
)
rowdependencies
;

alter table t1 add constraint t1_pk primary key(id1, id2) using index (
	create index t1_pk on t1(id1, id2) compress 1
);

create table t2(
	id1	number not null,
	id2	number not null,
	id3	number not null,
	n1	number,
	v1	varchar2(10)
)
rowdependencies
;

alter table t2 add constraint t2_fk_t1 foreign key(id1, id2) references t1;

It’s quite simple – I’ve got a multi-column primary key, and it’s worth compressing on the first column because that column is fairly repetitive. Then I’ve created another table that has a foreign key constraint referencing my first table. Because I’ve got some replication going on and want to enable parallelism I’ve enabled rowdependencies all over the place. So let’s insert a couple of rows and see what happens – the next bit of text is cut-n-pasted from an 11.2.0.4 SQL*Plus session running a script after a call to set echo on:

SQL> insert into t1 values(1,1,1,'x');

1 row created.

SQL> commit;

Commit complete.

SQL>
SQL> insert into t2 values(1,1,1,1,'x');
insert into t2 values(1,1,1,1,'x')
            *
ERROR at line 1:
ORA-00600: internal error code, arguments: [25027], [5], [394178], [], [], [], [], [], [], [], [], []

For further details, and before you get completely thrilled at the possibility of compressing lots of indexes, keep an eye on:

Bug 18125878 : ORA-600 [25027] ON INSERT IF TABLE HAS ROWDEPENDENCIES AND COMPRESS ON PK

“Inserting into a table with a foreign key where the base table has a primary key using index key compression and the table also has row dependencies enabled. Stack will include kdsgrds and kdiexi0 (in 12) / kdiexi (in 11, 10)”

As implied by that note from the bug, it also affects 10g.  The bug note reports it as fixed in 12.2.

Related posts:

1. Compression in Oracle – part 5: Costs of Index Compression
2. Compression in Oracle – part 4: Basic Index Compression
3. A few words on Index Compression
4. Index Hash
5. Index block split bug in 9i
6. Index block split bug in 9i
7. Compression in Oracle – Part 1: Basic Table Compression
8. Virtual Integrity
9. Index Hints
10. Virtual Column