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BUG/MINOR: hash-balance-factor isn't effective in certain circumstances

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in chash_get_server_hash, we find the nearest server entries both
before and after the request hash. If the next and prev entries both
point to the same server, the function would exit early and return that
server, to save work.

Before hash-balance-factor this was a valid optimization -- one of nsrv
and psrv would definitely be chosen, so if they are the same there's no
need to choose between them. But with hash-balance-factor it's possible
that adding another request to that server would overload it
(chash_server_is_eligible returns false) and we go further around the
ring. So it's not valid to return before checking for that.

This commit simply removes the early return, as it provides a minimal
savings even when it's correct.
This commit is contained in:
Andrew Rodland 2017-04-26 02:57:03 -04:00 committed by Willy Tarreau
parent e068b60605
commit 18330ab17f
1 changed files with 1 additions and 3 deletions
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4
src/lb_chash.c
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@ -306,10 +306,8 @@ struct server *chash_get_server_hash(struct proxy *p, unsigned int hash)
nsrv = eb32_entry(next, struct tree_occ, node)->server;
psrv = eb32_entry(prev, struct tree_occ, node)->server;
if (nsrv == psrv)
return nsrv;
/* OK we're located between two distinct servers, let's
/* OK we're located between two servers, let's
* compare distances between hash and the two servers
* and select the closest server.
*/