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Use dictGetFairRandomKey() for HRANDFIELD,SRANDMEMBER,ZRANDMEMBER (#9538)

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In the `HRANDFIELD`, `SRANDMEMBER` and `ZRANDMEMBER` commands,
There are some strategies that could in some rare cases return an unfair random.
these cases are where s small dict happens be be hashed unevenly.

Specifically when `count*ZRANDMEMBER_SUB_STRATEGY_MUL > size`,
using `dictGetRandomKey` to randomize from a dict will result in an unfair random result.
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sundb 2021-09-24 22:36:26 +08:00 committed by GitHub
parent bdecbd30df
commit 9967a53f4c
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3 changed files with 3 additions and 3 deletions
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2
src/t_hash.c
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@ -1046,7 +1046,7 @@ void hrandfieldWithCountCommand(client *c, long l, int withvalues) {
/* Remove random elements to reach the right count. */
while (size > count) {
dictEntry *de;
de = dictGetRandomKey(d);
de = dictGetFairRandomKey(d);
dictUnlink(d,dictGetKey(de));
sdsfree(dictGetKey(de));
sdsfree(dictGetVal(de));

2
src/t_set.c
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@ -754,7 +754,7 @@ void srandmemberWithCountCommand(client *c) {
/* Remove random elements to reach the right count. */
while (size > count) {
dictEntry *de;
de = dictGetRandomKey(d);
de = dictGetFairRandomKey(d);
dictUnlink(d,dictGetKey(de));
sdsfree(dictGetKey(de));
dictFreeUnlinkedEntry(d,de);

2
src/t_zset.c
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@ -4159,7 +4159,7 @@ void zrandmemberWithCountCommand(client *c, long l, int withscores) {
/* Remove random elements to reach the right count. */
while (size > count) {
dictEntry *de;
de = dictGetRandomKey(d);
de = dictGetFairRandomKey(d);
dictUnlink(d,dictGetKey(de));
sdsfree(dictGetKey(de));
dictFreeUnlinkedEntry(d,de);