Hi Boris, On 04/04/11 19:08, dbori...@hotmail.com wrote:
> I have (maybe silly) question about NULL mask. There are no silly questions! <SNIP> > First record NULL mask (Dpg_offset was 0x0FE0): > 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 mask should occupy 4 or 8 or 12 etc bytes. What am I missing? Nothing at all. There will be 23 zero bytes in this part of the page. However, they are simply padding in the case of the example record contents you supplied - two NULL fields. The data in entire record is effectively covered by the bits in the NULL mask. The zero bytes are most likely the initialised contents of the working buffer where the data was assembled before being written to the page. If you were to update the data in one or both of the columns, you would be able to examine the hex dump again and see that the NULL mask now shows not null, and the existing zeros will hold the compressed format of the new data. The NULL mask is a minimum of 4 bytes to allow for up to 32 fields. If there is 33 fields, then the NULL mask will consist of another 4 bytes, of which, only 1 single bit will be used. And so on, adding 4 bytes every time there is more than a multiple of 32 fields in a record. > > Thanks in advance and sorry for my English Your English is fine, trust me. I speak *only* English I'm ashamed to say. HTH Cheers, Norman. -- Norman Dunbar Dunbar IT Consultants Ltd Registered address: Thorpe House 61 Richardshaw Lane Pudsey West Yorkshire United Kingdom LS28 7EL Company Number: 05132767 ------------------------------------------------------------------------------ Create and publish websites with WebMatrix Use the most popular FREE web apps or write code yourself; WebMatrix provides all the features you need to develop and publish your website. http://p.sf.net/sfu/ms-webmatrix-sf _______________________________________________ Firebird-docs mailing list Firebird-docs@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/firebird-docs
