Notes about Redis

notes.md

Notes

• dbDictType used as argument to dictCreate in server.c (initServer)

• Uses dictSdsHash, dictSdsKeyCompare, dictSdsKeyDestructor, dictObjectDestructor

• dict struct:

  • dictType
  • privdata
  • ht (2 of them)
  • rehashidx
  • iterators

• dictht:

  • table (dictentry)
  • size
  • sizemask
  • used

• dictentry:

  • key
  • v (val, u64, s64, d)
  • next

• dictAdd

  • calls dictAddRaw
  • calls dictSetVal (a macro, sets the val to the entry)

• dictAddRaw (dict.c)

  • get the index with _dictKeyIndex and dictHashKey(d, key)
  • prepends the entry to ht->table with the index from the previous step, itself is a list of entries
  • calls dictSetKey (a macro, sets the key to entry)

• setGenericCommand (takes the key as argument, and the val)

  • called from ...

• genericSetKey (db.c)

  • calls dbAdd

• dbAdd (db.c)

  • calls dictAdd (dict.c)

• dictAdd (above)

• tryResizeHashTables is called from databasesCron

  • itself called from serverCron

• Two similar functions dictResize & dictExpand. Resize calls Expand

  • expand does the actual expand
  • resize figures out the size for you
  • Rehash Just sets up the second ht for rehashing (->rehashidx = 0)

• incrementallyRehash is called in databsesCron (server.c)

  • aaa

• rules for _dictExpandIfNeeded (called for every call to _dictKeyIndex)

  • Resize to 2x the size if used >= size && (can_resize || used/size > 5)
  • Resize will find the right size, so it might shrink it
  • Will resize if bigger than 4 but usage is below 10%

• dictHashKey is a macro (dict.h)

  • delegates to (d)->type->hashFunction (dictSdsHash here)

• dictSdsHash (in server.c)

  • calls dictGenHashFunction (in dict.c)

• dictGenHashFunction

  • calls siphash

• dictSetHashFunctionSeed

  • called in main (server.c) with hashseed, result of getRandomBytes

• _dictKeyIndex (in dict.c)