[bind10-dev] Blog comment from BDB developer

zhanglikun zlkzhy at gmail.com
Fri Jun 25 03:04:31 UTC 2010

> On Thu, 2010-06-24 at 18:00 +0000, Francis Dupont wrote:
> > > Best we contact them soon since we need additional functionality from
> > > BDB's C API to walk the zone backward as well as forward once we do a
> >
> > => the stupid answer is to create a cursor and to use it to get
> > with DB_NEXT / DB_PREV. Of course this means to set comparison
> > functions before... Now I am not an expert in BDB when a whole
> > group of experts propose their help (:-)!
> The problem with this is that we need the DB_NEXT/DB_PREV for handling
> NXDOMAIN in DNSSEC. But with the C API if you get no match you doing get
> a cursor back, you get a "no data found" return.
> Evan (I think) proposed a brilliant hack of:
>      1. Inserting a data record if no match is found
>      2. Looking up a cursor at that record
>      3. Using DB_PREV to get the covering NSEC value
>      4. Deleting the data record we added
> Clearly this is... sub-optimal. But I'm pretty sure it would work.
> A better solution would be what Michael alluded to, which is to have a
> lookup which returns "I didn't find the value you wanted, but this is
> the previous/next match in the data we have". We think that the Java API
> provides this functionality, so there should be no fundamental changes
> to BDB to support it.

Use the cursor with flag "DB_SET_RANGE", since the returned key/data pair is
the smallest key greater than or equal to the specified key.

see (Copied from BDB API documents):
The DB_SET_RANGE flag is identical to the DB_SET flag, except that in the
case of the Btree access method, the key is returned as well as the data
item and the returned key/data pair is the smallest key greater than or
equal to the specified key (as determined by the Btree comparison function),
permitting partial key matches and range searches.

So it will depends on how we design the key and key comparation function.


    Compare rr type first ,
    Then compare rr name, 

Define two non-exist types:

So find next name should query with  the key "TYPE_MAX + query_name"

Oh find the prev name is a little tricky:
    first query with the key "TYPE_NONE + query_name",  then move the cursor
to the prev one, oh, we find it.

Example, the records in bdb database is:
a.cn.   A
a.cn.   NS  a.a.cn.

c.cn.   A
c.cn.   NS  a.c.cn.

query with  TYPE_MAX + 'b.cn.',  will find "c.cn." directly.

Query with TYPE_NONE + 'b.cn.',  will find  c.cn. first, then move cursor
the prev one,  'a.cn. NS a.a.cn.' is found.

Hope this can provide some help, :)

Zhang Likun

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