Thanks Tony for the detailed answer! I just found the parts of the code you mentioned that related to the policy eviction.
There is something I can't figure out, What the Red Black Tree DB is used for and what the ADB is used for? Is there a relationship between the two? Sorry if the answers are pretty clear, I’m new to BIND. Itay On Mon, Dec 30, 2019, 22:07 Tony Finch <d...@dotat.at> wrote: > Itay Alayoff <itay...@post.bgu.ac.il> wrote: > > > I'd like to know where is the policy eviction currently implemented? > > The way I answer questions like this is to start from the configuration > options, and working my way from bin/named/server.c (where the parsed > config file is processed) I trace through to find the code that uses the > options of interest. Often with an option like `some-thing` I can find > most of the code by grepping for `some.?thing` but the spelling is not > always that consistent. > > In this case, grepping for `cache.?size` I can see a line: > > dns_cache_setcachesize(cache, max_cache_size); > > So (unsurprisingly!) the next place to look is in lib/dns/cache.c > where I find dns_cache_setcachesize() which sets up a callback function > called water() to implement the limits. In turn water() invokes > dns_db_overmem(). > > https://gitlab.isc.org/isc-projects/bind9/blob/master/lib/dns/cache.c#L880 > > There's an abstraction layer around BIND's in-memory database to support > alternative back ends (look around for dyndb and sdb to follow this > side-track) with a C OO interface that will feel familiar to kernel > hackers. But we want to skip to the relevant point which for db matters is > usually lib/dns/rbtdb.c, the red-black tree database. There are a bunch of > method vtbl definitions in this file; we're looking for the `overmem` > method. In fact, looking for `overmem` everywhere in the file should get > you a bit closer to enlightenment. > > https://gitlab.isc.org/isc-projects/bind9/blob/master/lib/dns/rbtdb.c > > The rbtdb.c overmem() method actually says, > > /* This is an empty callback. See adb.c:water() */ > > The adb (address database) handles stuff like SRTT calculations and > lameness flags etc. Reading around mentions of `overmem` and `water` > in adb.c is again informative. > > https://gitlab.isc.org/isc-projects/bind9/blob/master/lib/dns/adb.c#L2305 > > This comment appears to be the crux: > > /*% > * Examine the tail entry of the LRU list to see if it expires or is stale > * (unused for some period); if so, the name entry will be freed. If the > ADB > * is in the overmem condition, the tail and the next to tail entries > * will be unconditionally removed (unless they have an outstanding fetch). > * We don't care about a race on 'overmem' at the risk of causing some > * collateral damage or a small delay in starting cleanup, so we don't > bother > * to lock ADB (if it's not locked). > * > * Name bucket must be locked; adb may be locked; no other locks held. > */ > static void > check_stale_name(dns_adb_t *adb, int bucket, isc_stdtime_t now) { > > > Now you know everything I know about BIND's cache eviction policy :-) > > Tony. > -- > f.anthony.n.finch <d...@dotat.at> http://dotat.at/ > North Rockall, Malin: Northwesterly 4 or 5, backing southerly 5 to 7 later. > Rough. Fair. Good. > >
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