From a9caca0424197e1b43cc98c5106cca5c86e3ac34 Mon Sep 17 00:00:00 2001 From: antirez Date: Mon, 24 Mar 2014 09:38:33 +0100 Subject: [PATCH] sdscatvprintf(): guess buflen using format length. sdscatvprintf() uses a loop where it tries to output the formatted string in a buffer of the initial length, if there was not enough room, a buffer of doubled size is tried and so forth. The initial guess for the buffer length was very poor, an hardcoded "16". This caused the printf to be processed multiple times without a good reason. Given that printf functions are already not fast, the overhead was significant. The new heuristic is to use a buffer 4 times the length of the format buffer, and 32 as minimal size. This appears to be a good balance for typical uses of the function inside the Redis code base. This change improved INFO command performances 3 times. --- src/sds.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/sds.c b/src/sds.c index 64c9a961..ef0bb6bf 100644 --- a/src/sds.c +++ b/src/sds.c @@ -293,8 +293,9 @@ sds sdscpy(sds s, const char *t) { sds sdscatvprintf(sds s, const char *fmt, va_list ap) { va_list cpy; char *buf, *t; - size_t buflen = 16; + size_t buflen = strlen(fmt)*4; + if (buflen < 32) buflen = 32; while(1) { buf = zmalloc(buflen); if (buf == NULL) return NULL;