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object expiry tracking memroy usage
====================================
Bitrot daemon tracks objects for expiry in a data structure known
as "timer-wheel" (after which the object is signed). It's a well
known data structure for tracking million of objects of expiry.
Let's see the memory usage involved when tracking 1 million
objects (per brick).
Bitrot daemon uses "br_object" structure to hold information
needed for signing. An instance of this structure is allocated
for each object that needs to be signed.
struct br_object {
xlator_t *this;
br_child_t *child;
void *data;
uuid_t gfid;
unsigned long signedversion;
struct list_head list;
};
Timer-wheel requires an instance of the structure below per
object that needs to be tracked for expiry.
struct gf_tw_timer_list {
void *data;
unsigned long expires;
/** callback routine */
void (*function)(struct gf_tw_timer_list *, void *, unsigned long);
struct list_head entry;
};
Structure sizes:
sizeof (struct br_object): 64 bytes
sizeof (struct gf_tw_timer_list): 40 bytes
Together, these structures take up 104 bytes. To track all 1 million objects
at the same time, the amount of memory taken up would be:
1,000,000 * 104 bytes: ~100MB
Not so bad, I think.
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