[erlang-patches] New index type in mnesia (new feature)

aleksander.nycz <>
Fri Jun 21 18:35:26 CEST 2013


Hello,

Unfortunatelly patch in R16B01 does't fix all performance problem for low
cardinality columns.

I've prepared simple benchmark for otp_R16B, otp_R16B01 and otp_R16B01
with mnesia new index patch. File test.erl shouls be run on otp_R16B,
otp_R16B01
and test2.erl on otp_R16B01 with mnesia new index patch.
In atachement benchmark results from my laptop (ubuntu 13.04, 4 core, 4GB
RAM).

Please note that patch, that was applied in R1601 fix only problem with
insert operation (was bag in R16B, is duplicated_bag in R16B01):

{{TableType, Storage, IndexesAndType, Unused}, TransactionContext,
Operation, Records, OperationTime [us], Rec/sec}

otp_R16:
{{set,ram_copies,[state],[]},async_dirty,'Insert',10000,754401,13255.55},
otp_R16B01:
{{set,ram_copies,[state],[]},async_dirty,'Insert',10000,111412,89756.94},

but write and delete operations are still very slow:
{{set,ram_copies,[state],[]},async_dirty,'UpdateStateField',10000,3107059,3218.48},
{{set,ram_copies,[state],[]},async_dirty,'UpdatemTimeField',10000,2920105,3424.53},
  {{set,ram_copies,[state],[]},async_dirty,'Delete',10000,1445054,6920.16},

In my solution, there is no necessity to iterate long lists (in case of
low cardinality column), but Primary key value are deleted/inserted
from/info ets.

Below benchmark result for my solution with new index type:
{{set,ram_copies,{state,idx_ets},[]},async_dirty,'Insert',10000,122417,81688.00},
{{set,ram_copies,{state,idx_ets},[]},async_dirty,'UpdateStateField',10000,149560,66862.80},
  {{set,ram_copies,{state,idx_ets},[]},async_dirty,'UpdatemTimeField',10000,146501,68258.92},
  {{set,ram_copies,{state,idx_ets},[]},async_dirty,'Delete',10000,103037,97052.52}

Please run this benchmarks on your machine and check results.

Regards
Aleksander Nycz

> There is a patch included in the today's release that address this issue
> in
> a simpler way,
> for set (and ordered set if I remember correctly).
>
> Can you check if the performance is good enough for you in R16B01.
>
> /Dan
>
>
> On Wed, Jun 19, 2013 at 6:51 PM, Aleksander Nycz
> <
>> wrote:
>
>> Hello,
>>
>> Mnesia gives possibility to create table indexes, when
>> the user wants to frequently use some other field
>> than the key field to look up records.
>>
>> Current index solution in mnesia uses ets table (type bag or
>> duplicated_bag) to maintain mapping:
>> Indexed field value -> Primary key value.
>>
>> Unfortunatelly current solution has very significant disadvantage:
>> operation performance (loading table, insert new records,
>> delete records, etc.) is very low when index is set on 'Low-cardinality
>> column'
>>
>> http://en.wikipedia.org/wiki/**Cardinality_%28SQL_statements%**29<http://en.wikipedia.org/wiki/Cardinality_%28SQL_statements%29>
>>
>> In such case operation complexity is O(n) when n is number
>> of Primary Key Values. For small n performance can be acceptable for
>> some
>> application,
>> but when n is the hundreds, thousands or even more such index
>> are useless. New index type provides O(1) complexity.
>>
>> This patch introduces new index type in mnesia database.
>> Main concept is to maintain all Primary Key Values not direcly in
>> bag/duplicated_bag ets but in set of ets.
>> For each Indexed field value new ets is created
>> and Primary Key Values are strored in this ets.
>> For 'Low-cardinality column' there is only a few Indexed key value (eg.
>> isActive (true/false), state (new/pending/suspended/active)**, ...)
>> so memory overhead for ets is not significant.
>>
>> Standard index:
>>     Indexed field value -> [Primary key value]
>>
>> New index based on ets:
>>     Indexed field value -> ets, that contains Primary key value
>>
>> Restrictions:
>>
>> 1. New index can be created on disc_copies or ram_copies tables only.
>> Tables disc_only_copies are not supported.
>> 2. Index type can't be changed. The only way to change existing index
>> idx_list to idx_ets and vice versa
>>      is to delete existing index and create new one by
>> mnesia:add_table_index/3 (new function, see below)
>>
>>
>> New API:
>>
>> 1. Define index type when table is created:
>>
>> create_table(Name, TabDef) -> {atomic, ok} | {aborted, Reason}
>>
>> New TabDef value:
>> {index_type, [{atom() | int(), 'idx_std' | 'idx_ets'}]} - 'idx_std' is
>> default when index is created
>>
>> Example:
>>
>> -type(poolId() :: integer()).
>> -type(bucketId() :: integer()).
>> -type(resourceState() :: free | reserved | gracePeriod).
>>
>> -record(rmResource, {id                                 :: {poolId(),
>> any()}
>>                     ,state                              :: {poolId(),
>> bucketId(), resourceState()}
>>                     ,availableFrom                      :: integer()
>>                     ,availableTo                        :: integer()
>>                     ,requestorId                        :: any()
>>                     ,reservedFrom                       :: integer()
>>                     ,reservedTo                         :: integer()
>>                     ,isDeleted      = false             :: boolean()
>>                     ,mTime                              :: integer()}).
>>
>>      {atomic,ok} = mnesia:create_table(**tRMResources
>>                                       ,[
>>                                          {disc_copies, []}
>>                                         ,{ram_copies, [node()]}
>>                                         ,{type,set}
>> ,{attributes,record_info(**fields, rmResource)}
>>                                         ,{record_name, rmResource}
>>                                         ,{index, [state, requestorId,
>> mTime]}
>>                                         ,{index_type, [{state, idx_ets},
>> {requestorId, idx_std}]}
>>                                        ]),
>>
>> 2. Add new index to existing table:
>>
>> mnesia:add_table_index(Tab, AttrName, IndexOpts) -> {aborted, R} |
>> {atomic, ok}
>>
>> This function creates a index on Mnesia table called Tab on AttrName
>> field according to the argument IndexOpts.
>> This list must be a list of {Item, Value} tuples, currently only one
>> option is allowed:
>>      {index_type, 'idx_std' | 'idx_ets'}
>>
>> Example:
>>
>> mnesia:add_table_index(**tRMResources, isDeleted, [{index_type,
>> 'idx_ets'}])
>>
>> 3. New match_object/4, dirty_match_object/3 functions:
>>
>> match_object(Tab, Pat, Limit, LockKind) -> [Record] | transaction abort.
>> dirty_match_object(Tab, Pat, Limit) -> [Record] | exit({aborted,
>> Reason}).
>>
>> Similar to match_object/3 and dirty_match_object/2, but returns no more
>> than Limit records.
>>
>>
>> 4. New index_match_object/5, dirty_index_match_object/4 functions:
>>
>> index_match_object(Tab, Pat, Attr, Limit, LockKind) -> [Record] |
>> transaction abort.
>> dirty_index_match_object(Tab, Pat, Attr, Limit) -> [Record] |
>> exit({aborted, Reason}).
>>
>> Similar to index_match_object/4, dirty_index_match_object/3 but returns
>> no
>> more than Limit records.
>>
>>
>> 5. New index_read/4, dirty_index_read/4 functions:
>>
>> index_read(Tab, Key, Attr, Limit) -> [Record] | transaction abort.
>> dirty_index_read(Tab, Key, Attr, Limit) -> [Record] | exit({aborted,
>> Reason}).
>>
>> Similar to index_read/3, dirty_index_read/3 but returns no more than
>> Limit
>> records.
>>
>>
>> 6. New select_limit/3, select_limit/4, dirty_select/3 functions;
>>
>> select_limit(Tab, MatchSpec, NObjects [, Lock]) -> [Object] |
>> transaction
>> abort.
>>
>> Similar to select(Tab, MatchSpec [, Lock]) but returns maximum NObjects
>> records, of course empty list can also be returned.
>> Continuation (see select/4) is not possible. This function can also use
>> indexes to find matching records
>> as contrasted with select/4.
>>
>> dirty_select(Tab, Spec, Limit) -> [Object] | exit({aborted, Reason}.
>>
>> Similar to dirty_select/2 but returns no more than Limit records.
>>
>> And git links:
>>
>> git fetch
>> git://github.com/nyczol/otp.**git<http://github.com/nyczol/otp.git>mnesia_new_index
>>
>> https://github.com/nyczol/otp/**compare/erlang:master...**mnesia_new_index<https://github.com/nyczol/otp/compare/erlang:master...mnesia_new_index>
>> https://github.com/nyczol/otp/**compare/erlang:master...**
>> mnesia_new_index.patch<https://github.com/nyczol/otp/compare/erlang:master...mnesia_new_index.patch>
>>
>> Regards,
>> Aleksander Nycz
>>
>> --
>> Aleksander Nycz
>> Senior Software Engineer
>> Telco_021 BSS R&D
>> Comarch SA
>> Phone:  +48 12 646 1216
>> Mobile: +48 691 464 275
>> website: www.comarch.pl
>>
>>
>>
>> _______________________________________________
>> erlang-patches mailing list
>> 
>> http://erlang.org/mailman/listinfo/erlang-patches
>>
>>
>
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