Redis dict and_rehash
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Redis Dict Data Structure [email protected]
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Transcript of Redis dict and_rehash
Redis Insert Flow
dictAdd
dictSetVal
1. Redis uses two tables: table[0], table[1] 2. Tables have buckets for dictEntry
dictAddRaw
dictAddRaw
_dictKeyIndex
1. dictAddRaw actually makes new dirEntry. 2. If rehash is possbile, conduct rehashing. 3. _dictKeyIndex check the item is existed. If it is existed,
dictAddRaw will fail. 4. Used++
_dictSetKey
_dictRehashStep
dictRehashStep 1. dictRehash’s parameter n is the variable that how
many buckets will be rehashed. For performance, it is always 1.
2. If Ht[0]used is 0, rehashng is finished. Ht[0] = ht[1] and return;
3. while(d->ht[0].table[d->rehashidx] == NULL) d->rehashidx++; if current bucket is NULL, go next bucket.
4. Bucket size is always increased as twice.
5. And divide dictEntry with hashmask. For example, at the first time. mask is 3 and hash value 2, 5 were in same bucket . After doubling bucket size, mask will be 7, so hash value 2 will be in bucket #2, and 5 will be in bucket #5
dictRehash
Redis Dict is Hash
Dynamic Hash Expand twice
Linear probing
Bucket #0
Bucket #1
Bucket #2
Bucket #3
0
1
2
3
Add 0,1,2,3
Bucket #0
Bucket #1
Bucket #2
Bucket #3
4
1
2
3
Add 4 with line Probing
0
Bucket #0
Bucket #1
Bucket #2
Bucket #3
4
1
2
3
Rehashing with HT[1]
0
Bucket #0
Bucket #1
Bucket #2
Bucket #3
Bucket #4
Bucket #5
Bucket #6
Bucket #7
Bucket #0
Bucket #1
Bucket #2
Bucket #3
1
2
3
Rehashing one step #1
Bucket #0
Bucket #1
Bucket #2
Bucket #3
Bucket #4
Bucket #5
Bucket #6
Bucket #7
4
0
Used--; Used--;
After all rehashing
ht[0] = ht[1] reset ht[1] For next rehashing
