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From Daniel Chia <danc...@coursera.org>
Subject Re: Deserialize the collection type data from the SSTable file
Date Wed, 10 Jun 2015 16:11:02 GMT
Hi Yong,

Glad the code was helpful. I believe it serializes using
List<Pair<ByteBuffer, Column>> for maps so that it can store the Key of the
map as well.

Thanks for pointing out the edge case!

Thanks,
Daniel

On Wed, Jun 10, 2015 at 6:39 AM, java8964 <java8964@hotmail.com> wrote:

> Thanks, Daniel.
>
> I didn't realize that Cassandra will serialize one more way using
> List<Pair<ByteBuffer, Column>> for collection types. Reading your example
> code, I make it work.
>
> From link you gave me, using my test data, I found out one issue though.
> In any one row, if the collection column is NULL, I think the logic of code
> will throw NullPointException on line 148:
>
> Line 145    private void addValue(GenericRecord record, CFDefinition.Name name, ColumnGroupMap
group){Line 146        if (name.type.isCollection()) {Line 147            List<Pair<ByteBuffer,
Column>> collection = group.getCollection(name.name.key);Line 148            ByteBuffer
buffer = ((CollectionType)name.type).serialize(collection);
>             addCqlCollectionToRecord(record, name, buffer);
>
>
> If the collection column in that row is NULL, then Line 147 will return
> NULL, which will cause the following exception:
>
> Exception in thread "main" java.lang.NullPointerException
> at
> org.apache.cassandra.db.marshal.CollectionType.enforceLimit(CollectionType.java:113)
> at org.apache.cassandra.db.marshal.ListType.serialize(ListType.java:120)
>
> So I need to add a check to avoid that, as any regular columns in
> Cassandra could just have NULL value.
>
> Thanks
>
> Yong
>
> ------------------------------
> From: danchia@coursera.org
> Date: Mon, 8 Jun 2015 15:13:02 -0700
> Subject: Re: Deserialize the collection type data from the SSTable file
> To: user@cassandra.apache.org
>
>
> I'm not sure why sstable2json doesn't work for collections, but if you're
> into reading raw sstables we use the following code with good success:
>
>
> https://github.com/coursera/aegisthus/blob/77c73f6259f2a30d3d8ca64578be5c13ecc4e6f4/aegisthus-hadoop/src/main/java/org/coursera/mapreducer/CQLMapper.java#L85
>
> Thanks,
> Daniel
>
> On Mon, Jun 8, 2015 at 1:22 PM, java8964 <java8964@hotmail.com> wrote:
>
> Hi, Cassandra users:
>
> I have a question related to how to Deserialize the new collection types
> data in the Cassandra 2.x. (The exactly version is C 2.0.10).
>
> I create the following example tables in the CQLSH:
>
> CREATE TABLE coupon (
>   account_id bigint,
>   campaign_id uuid,
>   ........................,
>   discount_info map<text, text>,
>   ........................,
>   PRIMARY KEY (account_id, campaign_id)
> )
>
> The other columns can be ignored in this case. Then I inserted into the
> one test data like this:
>
> insert into coupon (account_id, campaign_id, discount_info) values
> (111,uuid(), {'test_key':'test_value'});
>
> After this, I got the SSTable files. I use the sstable2json file to check
> the output:
>
> $./resources/cassandra/bin/sstable2json /xxx/test-coupon-jb-1-Data.db
> [
> {"key": "000000000000006f","columns":
> [["0336e50d-21aa-4b3a-9f01-989a8c540e54:","",1433792922055000],
> ["0336e50d-21aa-4b3a-9f01-989a8c540e54:discount_info","0336e50d-21aa-4b3a-9f01-989a8c540e54:discount_info:!",1433792922054999,"t",1433792922],
> ["0336e50d-21aa-4b3a-9f01-989a8c540e54:discount_info:746573745f6b6579","746573745f76616c7565",1433792922055000]]}
> ]
>
> What I want to is to get the {"test_key" : "test_value"} as key/value pair
> that I input into "discount_info" column. I followed the sstable2json code,
> and try to deserialize the data by myself, but to my surprise, I cannot
> make it work, even I tried several ways, but kept getting Exception.
>
> From what I researched, I know that Cassandra put the "campaign_id" +
> "discount_info" + "Another ByteBuffer" as composite column in this case.
> When I deserialize this columnName, I got the following dumped out as
> String:
>
> "0336e50d-21aa-4b3a-9f01-989a8c540e54:discount_info:746573745f6b6579".
>
> It includes 3 parts: the first part is the uuid for the campaign_id. The
> 2nd part as "discount_info", which is the static name I defined in the
> table. The 3 part is a bytes array as length of 46, which I am not sure
> what it is.
>
> The corresponding value part of this composite column is another byte
> array as length of 10, hex as "746573745f76616c7565" if I dump it out.
>
> Now, here is what I did and not sure why it doesn't work.
> First, I assume the value part stores the real value I put in the Map, so
> I did the following:
>
> ByteBuffer value = ByteBufferUtil.clone(column.value());
>
> MapType<String, String> result = MapType.getInstance(UTF8Type.instance, UTF8Type.instance);
> Map<String, String> output = result.compose(value);
>
> // it gave me the following exception: org.apache.cassandra.serializers.MarshalException:
Not enough bytes to read a map
>
> Then I am think that the real value must be stored as part of the column names (the 3rd
part of 46 bytes), so I did this:
>
> MapType<String, String> result = MapType.getInstance(UTF8Type.instance, UTF8Type.instance);
> Map<String, String> output = result.compose(third_part.value);
>
> // I got the following exception:
>
> java.lang.IllegalArgumentException
> 	at java.nio.Buffer.limit(Buffer.java:267)
> 	at org.apache.cassandra.utils.ByteBufferUtil.readBytes(ByteBufferUtil.java:587)
> 	at org.apache.cassandra.utils.ByteBufferUtil.readBytesWithShortLength(ByteBufferUtil.java:596)
> 	at org.apache.cassandra.serializers.MapSerializer.deserialize(MapSerializer.java:63)
> 	at org.apache.cassandra.serializers.MapSerializer.deserialize(MapSerializer.java:28)
> 	at org.apache.cassandra.db.marshal.AbstractType.compose(AbstractType.java:142)
>
>
> I can get all other non-collection types data, but I cannot get the data from the Map.
My questions are:
>
> 1) How does the Cassandra store the collection data in the SSTable files? From the length
of bytes, it is most likely as part of the composite column. If so, why I got the exception
as above?
>
> 2) The sstable2json doesn't deserialize the real data out from the collection type. So
I don't have an example to follow. Do I use the wrong way trying to compose the Map type data?
>
>
> Thanks
>
>
> Yong
>
>
>

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