CODEWITHSUNDEEP
pythonzodb
Luke
Luke

Reputation: 1377

How to set cache size in ZODB?

I establish ZODB connection with the following code:

connection = ZODB.connection('zodb/connect4_reinf.fs')
dbroot = connection.root()

How can I set RAM cache size?

Upvotes: 1

Views: 456

Answers (2)

Victor von Cacahuete
Victor von Cacahuete

Reputation: 194

Regarding the connection between cache_size and cache_size_bytes (I'm posting this as an answer, since comments are a bit short for this purpose)

This time, we can find the answer in picklecache.py, again in the source code. After some renaming, it boils down to the following lines (in method _sweep):

for value in self.ring:
    if self.non_ghost_count <= target and (self.total_estimated_size <= target_size_bytes or not target_size_bytes):
            break
    (delete some objects from the cache)

here target is the cache_size of connection, in number of objects, and target_size_bytes is the cache_size_bytes passed to connection, in bytes. So in short, if cache_size_bytes evals to False (as the default value 0, but also None, etc...), only the number of objects is taken into account. If cache_size_bytes is present, both cache_size and cache_size_bytes are taken into account, and both conditions must apply, that is when an object must be brought into the cache, if the addition will lead to have more than cache_size living objects or more than cache_size_bytes bytes (estimated), some object will be deleted from the cache to make more room available.

Upvotes: 0

Victor von Cacahuete
Victor von Cacahuete

Reputation: 194

From the source code of class DB:

  def __init__(self, storage,
             pool_size=7,
             pool_timeout=1<<31,
             cache_size=400,
             cache_size_bytes=0,
             historical_pool_size=3,
             historical_cache_size=1000,
             historical_cache_size_bytes=0,
             historical_timeout=300,
             database_name='unnamed',
             databases=None,
             xrefs=True,
             large_record_size=1<<24,
             **storage_args):

When ZODB.connection is defined as follows:

def connection(*args, **kw):
    return DB(*args, **kw).open_then_close_db_when_connection_closes()

I would say

   connection = ZODB.connection('zodb/connect4_reinf.fs',
        cache_size=<your-cache-size>)

Also there's a cache_size_bytes if you prefer the limit to be in (estimated) bytes. 0 means unlimited for this parameter.

Upvotes: 2

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