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IDS Forum

RE: 11.70 data page slot table

Posted By: Madison Pruet
Date: Wednesday, 19 November 2014, at 6:27 p.m.

In Response To: RE: 11.70 data page slot table (Andrew Ford)

If the row has to move, then we update the index. But that is why we d=
on't
want to move rows unless we have to.

From: "Andrew Ford" <andrew@informix-dba.com>
To: ids@iiug.org
Date: 11/19/2014 03:36 PM
Subject: RE: 11.70 data page slot table [34200]
Sent by: ids-bounces@iiug.org

Did some additional testing if anyone is interested.

After an IPA, when a page on the older version is found and we have to =
move

a row to a new page because all rows no longer fit on a page we zero ou=
t
the
slot table entry for the row being updated and move that row to a new p=
age
and keep the original page unchanged (except for the change to the slot=

table). If you update the original page again, only then is the page is=

rewritten to reflect the new row length and complete the IPA.

Another question. Will Informix update indexes, etc. to reflect just th=
e
one
row being moved to a new page? It looks like it since there doesn't see=
m to

be any forwarding info stored in the slot table for that row, just the
first
2 bytes are zero'd out.

step 1

create table ipa_test (f1 char(151));
insert into ipa_test values ("1");
insert into ipa_test values ("2");
insert into ipa_test values ("3");
insert into ipa_test values ("4");
insert into ipa_test values ("5");
insert into ipa_test values ("6");
insert into ipa_test values ("7");
insert into ipa_test values ("8");
insert into ipa_test values ("9");
insert into ipa_test values ("10");
insert into ipa_test values ("11");
insert into ipa_test values ("12");
insert into ipa_test values ("13");

last 64 bytes of page: 13 slots

20202000 00000000 2c079700 95069700
fe059700 67059700 d0049700 39049700
a2039700 0b039700 74029700 dd019700
46019700 af009700 18009700 7a2973f6

step 2

alter table ipa_test add (f2 char(4));
update ipa_test set f1 =3D f1 where f1 =3D "7";

last 64 bytes of original page: 13 slots, slot 7 is zero'd out indicati=
ng
the row is not there. Otherwise the page is unchanged (i.e. row len in =
slot

table is still 151) and the original page is still flagged as the old
version, i.e. an in place alter is still pending.

20202000 00000000 2c079700 95069700
fe059700 67059700 d0049700 39049700
00009700 0b039700 74029700 dd019700
46019700 af009700 18009700 3a2a73f6

row "7" was moved to a new page with a row len of 155 in the slot table=
and

is flagged as the new version, i.e. not IPA pending

00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000
00000000 00000000 18009b00 3e2a73f6

step 3

update ipa_test set f1 =3D f1 where f1 =3D "6";

last 64 bytes of original page: 13 slots, slot 7 still zero'd out but r=
ow
len in slot table changed to 155 and page flagged as the new version

00000000 00000000 c1069b00 26069b00
8b059b00 f0049b00 55049b00 ba039b00
00009700 1f039b00 84029b00 e9019b00
4e019b00 b3009b00 18009b00 db2c73f6

-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
Madison Pruet
Sent: Wednesday, November 19, 2014 2:17 PM
To: ids@iiug.org
Subject: RE: 11.70 data page slot table [34198]

0x18 + 0x9b =3D3D 0xb3

From: "Andrew Ford" <andrew@informix-dba.com>
To: ids@iiug.org
Date: 11/19/2014 02:03 PM
Subject: RE: 11.70 data page slot table [34194] Sent by:
ids-bounces@iiug.org

Unless I'm confused about this page being updated (or how slots and dat=
=3D a
pages work), then why would there be 13 slots if only 12 rows fit in a
page.

Also, why would slot #3 indicate the row starts at byte 179 (0x00b3 =3D=
3D=3D
179)
when you'd expect the deleted row in slot #1 to start @ byte 24 right a=
=3D
fter

the header and the row in slot #2 to start at byte 179 (row size 155 + =
=3D
24 =3D3D

179).

Here is the last 64 bytes of a page that does not have a row delete and=
=3D
has

been updated after the IPA

00000000 00000000 c1069b00 26069b00
8b059b00 f0049b00 55049b00 ba039b00
1f039b00 84029b00 e9019b00 4e019b00
b3009b00 18009b00 00009700 daff72f6

and some oncheck -pP

addr stamp chksum nslots flag type frptr frcnt next prev
4:55 -160235558 99b 13 6801 DATA 1884 108
1000000 0

slot ptr len flg

2 24 155 0

3 179 155 0

4 334 155 0

5 489 155 0

6 644 155 0

7 799 155 0

8 954 155 0

9 1109 155 0

10 1264 155 0

11 1419 155 0

12 1574 155 0

13 1729 155 0

Andrew

-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
Madison Pruet
Sent: Wednesday, November 19, 2014 1:47 PM
To: ids@iiug.org
Subject: Re: 11.70 data page slot table [34192]

It looks to me like slot 1 and slot 2 are empty....

From: "Andrew Ford" <andrew@informix-dba.com>
To: ids@iiug.org
Date: 11/19/2014 01:23 PM
Subject: 11.70 data page slot table [34190] Sent by: ids-bounces@iiug.o=
=3D rg

Can anyone tell me what I'm looking at and why?

11.70 2K data page, row size is fixed at 155 bytes after in place alter=
=3D
=3D3D
(12

rows per page), previous row size was 151 bytes (13 rows per page), pag=
=3D
=3D3D
e has been updated after in place alter.

last 64 bytes of the 2K data page:

00000000 00000000 c1069b00 26069b00

8b059b00 f0049b00 55049b00 ba039b00

1f039b00 84029b00 e9019b00 4e019b00

b3009b00 00009b00 00009700 bd165df6

Last 4 bytes of the page is the checksum and I would expect the previou=
=3D
=3D3D
s
4
bytes to be slot #1 in the slot table entry, but it looks like it is
storing
the pre IPA size of the row (0x0097 =3D3D3D 151).

Preceding 12 sets of 4 bytes are the slot table entries (slot #2 to slo=
=3D
=3D3D
t #13, first row in the page at slot #2 has been deleted)

I guess my question is, when the page was rewritten to finalize the row=
=3D
=3D3D

alter why wasn't the slot table rewritten to be just 12 slots vs. keepi=
=3D
=3D3D
ng

13
slots and storing what appears to be the previous page size in slot #1.=
=3D
=3D3D

Thanks,

Andrew

***********************************************************************=
=3D
=3D3D
********

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=3D3D

***********************************************************************=
=3D
*****

***
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***********************************************************************=
=3D
********

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=3D

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*****

***
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********

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=

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