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networking: optimize parsing large bulk greater than 32k

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If we are going to read a large object from network
try to make it likely that it will start at c->querybuf
boundary so that we can optimize object creation
avoiding a large copy of data.

But only when the data we have not parsed is less than
or equal to ll+2. If the data length is greater than
ll+2, trimming querybuf is just a waste of time, because
at this time the querybuf contains not only our bulk.

It's easy to reproduce the that:

Time1: call `client pause 10000` on slave.

Time2: redis-benchmark -t set -r 10000 -d 33000 -n 10000.

Then slave hung after 10 seconds.
This commit is contained in:
zhaozhao.zz 2018-09-04 00:02:18 +08:00
parent febe102bf6
commit 247d2a734b
1 changed files with 13 additions and 10 deletions
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23
src/networking.c
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@ -1294,19 +1294,22 @@ int processMultibulkBuffer(client *c) {
c->qb_pos = newline-c->querybuf+2;
if (ll >= PROTO_MBULK_BIG_ARG) {
size_t qblen;
/* If we are going to read a large object from network
* try to make it likely that it will start at c->querybuf
* boundary so that we can optimize object creation
* avoiding a large copy of data. */
sdsrange(c->querybuf,c->qb_pos,-1);
c->qb_pos = 0;
qblen = sdslen(c->querybuf);
/* Hint the sds library about the amount of bytes this string is
* going to contain. */
if (qblen < (size_t)ll+2)
c->querybuf = sdsMakeRoomFor(c->querybuf,ll+2-qblen);
* avoiding a large copy of data.
*
* But only when the data we have not parsed is less than
* or equal to ll+2. If the data length is greater than
* ll+2, trimming querybuf is just a waste of time, because
* at this time the querybuf contains not only our bulk. */
if (sdslen(c->querybuf)-c->qb_pos <= (size_t)ll+2) {
sdsrange(c->querybuf,c->qb_pos,-1);
c->qb_pos = 0;
/* Hint the sds library about the amount of bytes this string is
* going to contain. */
c->querybuf = sdsMakeRoomFor(c->querybuf,ll+2);
}
}
c->bulklen = ll;
}