I have games table.
To keep it simple, I will add only two fields for the question.
gameId:
deadlineToPlay:
I want to query for all games with deadlineToPlay > than today.
How would I set up the index for this? I thought I could create an index with just deadlineToPlay, but if I understand correctly when querying on hashkey, it has to be exact value. Can't use >.
I would also not like to use a scan, due to costs.
A way to workaround this would be to create or use an existing field which will have constant value (for example, field hasDeadline with value true).
Now you can create the table key like this: hasDeadline as HASH key and deadlineToPlay as SORT key (if the table is already created, you can define this key in a new GSI).
This way you will be able to query by hasDeadline = true and deadlineToPlay > today.
Related
I've been reading a DynamoDB docs and was unable to understand if it does make sense to query on Global Secondary Index with a usage of 'contains' operator.
My problem is as follows: my dynamoDB document has a list of embedded objects, every object has a 'code' field which is unique:
{
"entities":[
{"code":"entity1Code", "name":"entity1Name"},
{"code":"entity2Code", "name":"entity2Name"}
]
}
I want to be able to get all documents that contain entities with entity.code = X.
For this purpose I'm considering adding a Global Secondary Index that would contain all entity.codes that are present in current db document separated by a comma. So the example above would look like:
{
"entities":[
{"code":"entity1Code", "name":"entity1Name"},
{"code":"entity2Code", "name":"entity2Name"}
],
"entitiesGlobalSecondaryIndex":"entityCode1,entityCode2"
}
And then I would like to apply filter expression on entitiesGlobalSecondaryIndex something like: entitiesGlobalSecondaryIndex contains entityCode1.
Would this be efficient or using global secondary index does not make sense in this way and DynamoDB will simply check the condition against every document which is similar so scan?
Any help is very appreciated,
Thanks
The contains operator of a query cannot be run on a partition Key. In order for a query to use any sort of operators (contains, begins with, > < ect...) you must have a range attributes- aka your Sort Key.
You can very well set up a GSI with some value as your PK and this code as your SK. However, GSIs are replication of the table - there is a slight potential for the data ina GSI to lag behind that of the master copy. If the query you're doing against this GSI isn't very often, then you're probably safe from that.
However. If you are trying to do this to the entire table at once then it's no better than a scan.
If what you need is a specific Code to return all its documents at once, then you could do a GSI with that as the PK. If you add a date field as the SK of this GSI it would even be time sorted. If you query against that code in that index, you'll get every single one of them.
Since you may have multiple codes, if they aren't too many per document, you maybe could use a Sparse Index - if you have an entity with code "AAAA" then you also have an attribute named AAAA (or AAAAflag or something.) It is always null/does not exist Unless the entities contains that code. If you do a GSI on this AAAflag attribute, it will only contain documents that contain that entity code, and ignore all where this attribute does not exist on a given document. This may work for you if you can also provide a good PK on this to keep the numbers well partitioned and if you don't have too many codes.
Filter expressions by the way are different than all of the above. Filter expressions are run on tbe data that would be returned, after it is already read out of the table. This is useful I'd you have a multi access pattern setup, but don't want a particular call to get all the documents associated with a particular PK - in the interests of keeping the data your code is working with concise. The query with a filter expression still retrieves everything from that query, but only presents what makes it past the filter.
If are only querying against a particular PK at any given time and you want to know if it contains any entities of x, then a Filter expressions would work perfectly. Of course, this is only per PK and not for your entire table.
If all you need is numbers, then you could do a count attribute on the document, or a meta document on that partition that contains these values and could be queried directly.
Lastly, and I have no idea if this would work or not, if your entities attribute is a map type you might very well be able to filter against entities code - and maybe even with entities.code.contains(value) if it was an SK - but I do not know if this is possible or not
We currently have a table that has both a partition key and sort key that make up the primary key.
They're both strings.
Example:
p_id: A#2021-04-21 (+)
s_id: XYZ#2#1634925978 (, , )
A use case of ours is to get all items for a given partition (regioncode+date), but ONLY the latest for a given id and code.
So for example if we had:
A#2021-04-21 , XYZ#2.0#10000 , <other attributes>
A#2021-04-21 , XYZ#2.0#20000 , ...
A#2021-04-21 , QRS#2.0#10000 , ...
We'd only want to get
A#2021-04-21 , XYZ#2.0#20000 , ...
A#2021-04-21 , QRS#2.0#10000 , ...
To do this currently, I'm just doing:
response = self.table.query(
KeyConditionExpression=Key(self.table_key_name).eq(f"{region_id}#{date_key}")
)
And then getting out the items, and having to manually make a map for each sort key prefix up until the epoch milliseconds / timestamp. Then for each key, set the value only if the timestamp is newer than whatever was previously there.
Is there a way to do this faster and utilize the query itself more? I've debated adding the pieces in the ID as attributes and maybe being able to use some kind of filtering but I don't think I see anything that would let me do the equivalent of a "group by" like I want here. Do I have no choice but to create some kind of Index?
Any ideas? Help would be much appreciated!
DDB doesn't support aggregations, MIN/MAX/COUNT/SUM/, like an RDBMS does...
One solution, is to use a "trigger", DDB Streams + Lamdba, to aggregate the needed data for you. See Using Global Secondary Indexes for Materialized Aggregation Queries
You might also want to consider looking at various ways to implement versioning of your DDB data.
If you want to get the latest item, then your Sort Key should end in an ISO8601 standard format date that is determined when the item is added. You can then do a Query and because your sort key is ending in an iso8601 standard date, the first item returned is automatically the last item added. (ISO8601 date format being 'alphabetical' and Sort Keys being ... well automatically sorted'. (and if you tell it to order the response in the opposite direction, then the first item returned is automatically... the first item!)
You will need to do something like SK: SOME_QUALIFIER#YYYY-mm-ddTHH:MM:SSZ00:00 - and then do your query with your SK begins with "SOME_QUALIFIER#". - so you will have to think about how you want to organize this, but it is entirely possible to do taking advantage of the fact that the sort key is automatically sorted.
Alternatively, if you are only going to be doing this once in a while (ie for a generated report or someting) Its OK to put your last updated date (or last created, which ever is more important) in its own attribute (And with composoite type keys you often should anyways!!!) and then create an index with that as your sort key, and something else (either report Type or something) for your PK. Then you can query that PK and get the latest item there
MIN/MAX and many other sql style calls can be tricked by making clever use of the sort key.
I have a dynamo table with the following attributes :
id (Number - primary key )
title (String)
created_at (Number - long)
tags (StringSet - contains a set of tags say android, ios, etc.,)
I want to be able to query by tags - get me all the items tagged android. How can I do that in DynamoDB? It appears that global secondary index can be built only on ScalarDataTypes (which is Number and String) and not on items inside a set.
If the approach I am taking is wrong, an alternative way for doing it either by creating different tables or changing the attributes is also fine.
DynamoDB is not designed to optimize indexing on set values. Below is a copy of the amazon's relevant documentation (from Improving Data Access with Secondary Indexes in DynamoDB).
The key schema for the index. Every attribute in the index key schema
must be a top-level attribute of type String, Number, or Binary.
Nested attributes and multi-valued sets are not allowed. Other
requirements for the key schema depend on the type of index: For a
global secondary index, the hash attribute can be any scalar table
attribute. A range attribute is optional, and it too can be any scalar
table attribute. For a local secondary index, the hash attribute must
be the same as the table's hash attribute, and the range attribute
must be a non-key table attribute.
Amazon recommends creating a separate one-to-many table for these kind of problems. More info here : Use one to many tables
This is a really old post, sorry to revive it, but I'd take a look at "Single Table Design"
Basically, stop thinking about your data as structured data - embrace denormalization
id (Number - primary key )
title (String)
created_at (Number - long)
tags (StringSet - contains a set of tags say android, ios, etc.,)
Instead of a nosql table with a "header" of this:
id|title|created_at|tags
think of it like this:
pk|sk |data....
id|id |{title, created_at}
id|id+tag|{id, tag} <- create one record per tag
You can still return everything by querying for pk=id & sk begins with id and join the tags to the id records in your app logic
and you can use a GSI to project id|id+tag into tag|id which will still require you to write two queries against your data to get items of a given tag (get the ids then get the items), but you won't have to duplicate your data, you wont have to scan and you'll still be able to get your items in one query when your access pattern doesn't rely on tags.
FWIW I'd start by thinking about all of your access patterns, and from there think about how you can structure composite keys and/or GSIs
cheers
You will need to create a separate table for this query.
If you are interested in fetching all items based on a tag then I suggest keeping a table with a primary key:
hash: tag
range: id
This way you can use a very simple Query to fetch all items by tag.
I wanted to run a query, "Find me the item with smallest 'id' which is larger than some number" ?
Is it possible in dynamodb ?
And how to do it ?
Thanks in advance.
As you probably know, a DynamoDB table can have 2 types of keys: hash keys, or hash+range keys
When you run a query, you need to specify the hash key for the item that you are looking for. If your table has a key of type hash+range, you will automatically get the results back with the range attribute sorted. Your Query request can also optionally add a KeyCondition on the range attribute so that you can require that it be larger than some number. So, yes, what you are looking for is possible, assuming that you design your table appropriately.
For more info, check out the following links:
http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html
http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/QueryAndScan.html
I have a table which has two varchar(Max) columns
Column 1 Column 2
-----------------------
URLRewitten OriginalURL
its part of my url re-writing for an asp.net webforms site.
when a url comes in I do a check to see if its in the table if it is i use the OriginalURL.
My question is, if all I'm doing is querying the table for urls and no other table in the database will ever link to this table does it need a dedicated primary key field? like an auto-number? will this make queries faster?
and also how can I make the query's run as faster?
Edit: I do have a unique constraint on URLRewitten.
Edit: ways i'm using this table..
Query when a new Request comes in.. search on URLRewitten to find OriginalURL
When needing to display a link on the site, i query on the OriginalURL to find the URLRewitten url i should use.
When adding a new url to the table i make sure that it doesn't already exist.
thats all the querys i do.. at the moment.
Both columns together would be unique.
Do you need a primary key? Yes. Always. However, it looks like in your case OriginalURL could be your primary key (I'm assuming that there wouldn't be more than one value for URLRewritten for a given value in OriginalURL).
This is what's known as a "natural key" (where a component of the data itself is, by its nature, unique). These can be convenient, though I have found that they're generally more trouble than they're worth under most circumstances, so yes, I would recommend some sort of opaque key (meaning a key that has no relation to the data in the row, other than to identify a single row). Whether or not you want an autonumber is up to you. It's certainly convenient, though identity columns come with their own set of advantages and disadvantages.
For now I suppose I would advise creating two things:
A primary key on your table of an identity column
A unique constraint on OriginalURL to enforce data integrity.
I'd put one in there anyway... it'll make updating alot easier or duplicating an existing rule...
i.e. this is easier
UPDATE Rules SET OriginalURL = 'http://www.domain.com' WHERE ID = 1
--OR
INSERT INTO Rules SELECT OriginalUrl, NewUrl FROM Rules WHERE ID = 1
Than this
this is easier
UPDATE Rules SET OriginalURL = "http://www.domain.com" WHERE OriginalURL = 'http://old.domain.com'
--OR
INSERT INTO Rules SELECT OriginalUrl, NewUrl FROM Rules WHERE OriginalURL = 'http://old.domain.com'
In terms of performance, if your going to be searching by OriginalURL,
you should add an index to that column,
I would use the OriginalURL as your primary key as I would assume this is unique. Assuming your are using SQL-Server you could create an index on RewrittenURL with OrigionalURL as an "Included column" to speed up the performance of the query.
An identity column can help when you search for recent events:
select top 100 * from table order by idcolumn desc
We'd have to know what kind of queries you are running, before we can search for a way to make them faster.
As you are doing your query on the URLRewritten column I don't think adding an auto-generated primary key would help you.
Have you got an index on your URLRewritten column? If not, create one: that should see a big increase in the speed of your queries (perhaps just make URLRewritten your primay key?).
Yes there should be a Primary Key Because you can set INDEX on that Primary Key for Fast Access
I don't think adding auto generated primary key will make your query faster.
However there are are a few things to consider:
I would not be so sure, that never
ever nothing will link to this table
:(.
I've seen a lot of people asking about
how to i.e. remove duplicates from
table like that -- with primary key
it is much easier.
To make this query
faster we need to
know more about this table and ways
of using it...
In my opinion, every table, must have auto generated primary key (i.e. identity in MSSQL).
I don't believe in unique natural keys.