I have (maybe silly) question about NULL mask. I write a Delphi program
(for my study) related to Firebird 2.1.3 ODS.
After examining Firebird internals and some posts on firebird-devel,
i've done some tests. I have a table named TEST with two fields
TEST1 char(10) and
TEST2 char(10).
I've inserted following data into table TEST:
('abc', 'def')
('aaaAAA', NULL)
(NULL, NULL).
On the bottom of the Data page, there are following hex values:
...
000A4FA0 | 00 00 00 00 00 00 00 00 00 00 00 00 80 01 00 00 |
............€...
000A4FB0 | 00 00 00 00 00 00 00 00 01 01 FF E9 00 00 00 00 |
..........ÿé....
000A4FC0 | 00 00 00 00 48 01 00 00 00 00 00 00 00 00 00 00 |
....H...........
000A4FD0 | 01 01 FE FD 00 FD 61 FD 41 FC 20 F6 00 00 00 00 | ..þý.ýaýAü
ö....
000A4FE0 | 41 01 00 00 00 00 00 00 00 00 00 00 01 01 FC FD |
A.............üý
000A4FF0 | 00 03 61 62 63 F9 20 03 64 65 66 F9 20 00 00 00 | ..abcù
.defù ...
First record NULL mask:
01 FC FD 00 (FC 00 00 00) - OK,
Second record NULL mask:
01 FE FD 00 (FE 00 00 00) - OK
Third record NULL mask:
01 FF E9 00 -??? - this part I do not understand.
If I understand correctly, there is E9 (23) bytes with zeros in NULL
mask? NULL nask should occupy 4 or 8 or 12 etc bytes. What am I missing?
Thanks in advance and sorry for my English.
Boris.
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