- direct-rdata-storage, move notes to header file comments.

dns.h

@@ -257,6 +257,58 @@ struct nsd_rdata_descriptor {
 																			 //    >> we'll see!
 };
 
+/*
+RDATA minimization is outlined in https://github.com/k0ekk0ek/database-case.
+
+The basic premise is that RDATA is directly allocated with the RR structure
+and that pointers to domains are directly stored (likely unaligned) in the
+RDATA. We do this primarily to save memory, but as the RDATA is directly
+stored with the RR, it is likely that data is cached with the RR which should
+have a positive impact on performance. When paired with direct conversion
+routines we are very likely to improve performance when importing zones and
+writing RRs out to the wire.
+
+The original idea was to implement conversion routines for type, but upon
+propagating changes throughout the codebase it turns out we have to do
+convert between more formats that just wire-to-internal, internal-to-wire,
+and internal-to-text. The result is an explosion in code.
+Consider the following matrix.
+
+
+* compressed wire format
+* uncompressed wire format
+* internal format
+* presentation format
+* generic presentation format (though mostly important for loading)
+
+For incremental zone transfers we convert from presentation format to
+uncompressed wire format to internal format to uncompressed wire format on
+loading. When writing out to the network we convert from uncompressed wire
+format to compressed wire format.
+
+The idea is that we can at least skip uncompressed wire format to internal
+format on loading, though we do have to normalize the domain names in the
+data (or assume that users won't update the on-disk data in which case we
+may trust the data gets written in normalized fashion). However, the
+uncompressed wire format to compressed wire format remains necessary.
+
+For conversion from uncompressed/compressed wire format to internal we make
+the interface such that a packet buffer is required and use
+dname\_make\_from\_packet so that the same import routines can be used.
+For internal to compressed wire format we implement a specialized routine so
+that answering of queries is as optimal as can be.
+
+For all other conversions, speed is not as important so the proposal is that
+we keep the descriptor table more-or-less as-is.
+
+For converting to (generic) presentation format, I propose we move that code
+to simdzone. The benefit there being that support for everything presentation
+format is in one place. The idea is that the interface is uncompressed wire
+format, so writing data out, the internal representation must replace the
+domain pointers by the uncompressed domain name in wire format.
+ */
+
+
 typedef struct nsd_type_descriptor nsd_type_descriptor_t;
 struct nsd_type_descriptor;