Defines mnesia_frag_hash callback behavior
This module defines a callback behavior for user-defined hash functions of fragmented tables.
Which module that is selected to implement the mnesia_frag_hash
behavior for a particular fragmented table is specified together
with the other frag_properties
. The hash_module
defines
the module name. The hash_state
defines the initial hash state.
This module implements dynamic hashing, which is a kind of hashing that grows nicely when new fragments are added. It is well suited for scalable hash tables.
Functions
Tab = atom()
State = term()
NewState = term()
Reason = term()
Starts when a fragmented table is
created with the function mnesia:create_table/2
or
when a normal (unfragmented) table is converted to be a
fragmented table with mnesia:change_table_frag/2
.
Notice that the function add_frag/2
is started
one time for each of the other fragments (except number 1)
as a part of the table creation procedure.
State
is the initial value of the hash_state
frag_property
. NewState
is stored as
hash_state
among the other frag_properties
.
State = term()
NewState = term()
IterFrags = [integer()]
AdditionalLockFrags = [integer()]
Reason = term()
To scale well, it is a good idea to ensure that the records are evenly distributed over all fragments, including the new one.
NewState
is stored as hash_state
among the
other frag_properties
.
As a part of the add_frag
procedure, Mnesia iterates
over all fragments corresponding to the IterFrags
numbers
and starts key_to_frag_number(NewState,RecordKey)
for
each record. If the new fragment differs from the old
fragment, the record is moved to the new fragment.
As the add_frag
procedure is a part of a schema
transaction, Mnesia acquires write locks on the
affected tables. That is, both the fragments corresponding
to IterFrags
and those corresponding to
AdditionalLockFrags
.
State = term()
NewState = term()
IterFrags = [integer()]
AdditionalLockFrags = [integer()]
Reason = term()
NewState
is stored as hash_state
among the
other frag_properties
.
As a part of the del_frag
procedure, Mnesia iterates
over all fragments corresponding to the IterFrags
numbers
and starts key_to_frag_number(NewState,RecordKey)
for
each record. If the new fragment differs from the old
fragment, the record is moved to the new fragment.
Notice that all records in the last fragment must be moved to another fragment, as the entire fragment is deleted.
As the del_frag
procedure is a part of a schema
transaction, Mnesia acquires write locks on the
affected tables. That is, both the fragments corresponding
to IterFrags
and those corresponding to
AdditionalLockFrags
.
FragNum = integer()
Reason = term()
Starts whenever Mnesia needs to determine
which fragment a certain record belongs to. It is typically
started at read
, write
, and delete
.
MatcSpec = ets_select_match_spec()
FragNums = [FragNum]
FragNum = integer()
Reason = term()
This function is called whenever Mnesia needs to determine
which fragments that need to be searched for a MatchSpec
.
It is typically called by select
and
match_object
.