Anyone with experience of adding new Storage backend for JanusGraph ? [Help needed w.r.t SnowFlake]

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Debasish Kanhar

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Oct 24, 2019, 4:27:34 PM10/24/19
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I know that JanusGraph needs a column-family type nosql database as storage backend, and hence that is why we have Scylla, Cassandra, HBase etc. SnowFlake isn't a column family database, but it has a column data type which can store any sort of data. So we can store complete JSON Oriented Column family data here after massaging / pre-processing the data. Is that a practical thought? Is is practical enough to implement?

If it is practical enough to implement, what needs to be done? I'm going through the source code, and I'm basing my ideas based on my understanding from janusgraph-cassandra and janusgraph-berkley projects. Please correct me if I'm wrong in my understanding.

  1. We need to have a StoreManager class like HBaseStoreManager, AbstractCassandraStoreManager, BerkeleyJEStoreManager which extends either DistributedStoreManager or LocalStoreManagerand implements KeyColumnValueStoreManager class right? These class needs to have build features object which is more or less like storage connection configuration. They need to have a beginTransaction method which creates the actual connection to corresponding storage backend. Is that correct?
  2. You will need to have corresponding Transaction classes which create the transaction to corresponding backend like *CassandraTransaction* or *BerkeleyJETx*. The transaction class needs to extend AbstractStoreTransaction` class. Though I can see and understand the transaction being created in BerkeleyJETx I don't see something similar for CassandraTransaction. So am I missing something in my undesrtanding here?
  3. You need to have KeyColumnValueStore class for backend. Like *AsyntaxKeyColumnValueStore* or *BerkeleyJEKeyValueStore* etc. They need to extend KeyColumnValueStore . This class takes care of massaging the data into KeyColumnFormat so that they can then be inserted into corresponding table inside Storage Backend.
    1. So question to my mind are, what will be structure of those classes?
    2. Are there some methods which needs to be present always like I see getSlice() being used across in all classes. Also, how do they work?
    3. Do they just convert incoming gremlin queries into KeyColumnValue structure?
    4. Are there any other classes I'm missing out on or these 3 are the only ones needed to be modified to create a new storage backend?
    5. Also, if these 3 are only classes needed, and let's say we success in using SnowFlake as storage backend, how do the read aspect of janusgraph/query aspect gets solved? Are there any changes needed as well on that end or JanusGraph is so abstracted that it can now start picking up from new source?
  4. And, I thought there would be some classes which would be reading in from "gremlin queries" doing certain "pre-processing into certain data structures (tabular)" and then pushed it through some connection into respective backends. This is where we cant help, is there a way to visualize those objects after "pre-processing"  and then store those objects as it is in SnowFlake and reuse it to fulfill gremlin queries.

I know we can store random objects in SnowFlake, just looking at changed needed at JanusGraph level to achieve those.

Any help will be really appreciated.

Thanks in Advance.

Dmitry Kovalev

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Oct 24, 2019, 5:47:24 PM10/24/19
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Hi Debashish,

here are my 2 cents:

First of all, you need to be clear with yourself as to why exactly you want to build a new backend? E.g. do you find that the existing ones are sub-optimal for certain use cases, or they are too hard to set up, or you just want to provide a backend to a cool new database in the hope that it will increase adoption, or smth else? In other words, do you have a clear idea of what is this new backend going to provide which the existing ones do not, e.g. advanced scalability or performance or ease of setup, or just an option for people with existing Snowflake infra to put it to a new use?

Second, you are almost correct, in that basically all you need to implement are three interfaces:
- KeyColumnValueStoreManager, which allows opening multiple instances of named KeyColumnValueStores and provides a certain level of transactional context between different stores it has opened
-  KeyColumnValueStore - which represents an ordered collection of "rows" accessible by keys, where each row is a
- KeyValueStore - basically an ordered collection of key-value pairs, which can be though of as individual "columns" of that row, and their respective values

Both row and column keys, and the data values are generic byte data.

Have a look at this piece of documentation: https://docs.janusgraph.org/advanced-topics/data-model/    

Possibly the simplest way to understand the "minimum contract" required by Janusgraph from a backend is to look at the inmemory backend. You will see that:  
- KeyColumnValueStoreManager is conceptually a Map of store name ->  KeyColumnValueStore, 
- each  KeyColumnValueStore is conceptually a NavigableMap of "rows" or KeyValueStores (i.e. a "table") ,
- each KeyValueStore is conceptually an ordered collection of key -> value pairs ("columns").

In the most basic case, once you implement these three relatively simple interfaces, Janusgraph can take care of all the translation of graph operations such as adding vertices and edges, and of gremlin queries, into a series of read-write operations over a collection of KCV stores. When you open a new graph, JanusGraph asks the KeyColumnValueStoreManager implementation to create a number of specially named KeyColumnValueStores, which it uses to store vertices, edges, and various indices. It creates a number of "utility" stores which it uses internally for locking, id management etc.

Crucially, whatever stores Janusgraph creates in your backend implementation, and whatever it is using them for, you only need to make sure that you implement those basic interfaces which allow to store arbitrary byte data and access it by arbitrary byte keys.

So for your first "naive" implementation, you most probably shouldn't worry too much about translation of graph model to KCVS model and back - this is what Janusgraph itself is mostly about anyway. Just use StoreFeatures to tell Janusgraph that your backend supports only most basic operations, and concentrate on thinking how to best implement the KCVS interfaces with your underlying database/storage system.

Of course, after that, as you start thinking of supporting better levels of consistency/transaction management across multiple stores, about performance, better utilising native indexing/query mechanisms, separate indexing backends, support for distributed backend model etc etc - you will find that there is more to it, and this is where you can gain further insights from the documentation, existing backend sources and asking more specific questions.

See for example this piece of documentation: https://docs.janusgraph.org/advanced-topics/eventual-consistency/

Hope this helps,
Dmitry

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Dmitry Kovalev

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Oct 24, 2019, 6:14:28 PM10/24/19
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One more useful pointer - CQLKeyColumnValueStore is a nice and compact example of how the discussed KCVS interface can be implemented on top of Cassandra, using prepared CQL statements

Debasish Kanhar

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Nov 27, 2019, 6:18:55 AM11/27/19
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Hi Dimitriy,

Sorry about the late response. I was working on this project part time only till last week when we moved into full time dev for this PoC. Really thanks to your pointers and Jason's that we have been able to start with the development works and we have some ground work to start with :-)

So,we are modelling SnowFlake (Which is like SQL File store) as a Key-Value store by creating two columns namely "Key" and "Value" in each tables. We are going to define the data type as binary here (Or Stringified Binary) so that arbitrary data can be dumped (I feel its of type StaticBuffer Key and StaticBuffer value. Is that correct? )

Since, we are modelling SnowFlake as Key-Value store, it makes sense to have a SnowFlakeManager class implement OrderedKeyValueStore like for BerkleyJE? Is that correct understanding?

Updates are that we have almost finished development of SnowFlakeManager class. The required methods needed are implemented like beginTransaction, openDatabase though one particular function not done is mutateMany is not done, but it will be done as it in turn calls KeyValueStore.insert() method.

Also, a lot of basic functions in KeyValueStore is also done like insert (Insert binary key-value), get (Get from binary key), delete (Delete a row using binary key). We are kinda stuck at the function getSlice(). What does it do?

We are kinda wondering how getSlice operates? I know that the function is used when querying Janusgraph for gremlin queries (Read operations) (https://github.com/BillBaird/delftswa-aurelius-titan/blob/master/SA-doc/Operations.md#queries) . We see that a sliceQuery is generated which is then executed againt backend to get results.
Now, my question here is that, slice query is used while queryingfor properties for vertices (edges/properties) by slicing the relations of vertex and slicing them based on filters/conditions. The following steps are followed in getSlice function (BerkleyKeyValueStore - berkleydb & ColumnValueStore - inmemory) :
  1. Find the row from the passed key. (Returns a Binary value against the binary key)
  2. Fetch slice bounderies, i.e. slice start and end from query passed
  3. Apply the slice boundries on the returned value in 1st step else, fetch the first results (pt 1) by applying the slicing conditions in step
My question is related to last step. Since my data in DB is just "Binary Key-Binary Value", how can we apply another constraints (slice conditions) in query? It just doesn't have any additional meta data to apply slice on as I just have 2 columns in my table.

Hope my explaination was clear for you to understand. I want to know primarily how the last step would work in the data model I described above (Having 2 columns, one for Key and other for Value. And each of stringified binary data type). And, is the data model selected good enough?

Thanks in advance. And I promise this time my replies will be quicker :-)

On Friday, 25 October 2019 03:17:24 UTC+5:30, Dmitry Kovalev wrote:
Hi Debashish,

here are my 2 cents:

First of all, you need to be clear with yourself as to why exactly you want to build a new backend? E.g. do you find that the existing ones are sub-optimal for certain use cases, or they are too hard to set up, or you just want to provide a backend to a cool new database in the hope that it will increase adoption, or smth else? In other words, do you have a clear idea of what is this new backend going to provide which the existing ones do not, e.g. advanced scalability or performance or ease of setup, or just an option for people with existing Snowflake infra to put it to a new use?

Second, you are almost correct, in that basically all you need to implement are three interfaces:
- KeyColumnValueStoreManager, which allows opening multiple instances of named KeyColumnValueStores and provides a certain level of transactional context between different stores it has opened
-  KeyColumnValueStore - which represents an ordered collection of "rows" accessible by keys, where each row is a
- KeyValueStore - basically an ordered collection of key-value pairs, which can be though of as individual "columns" of that row, and their respective values

Both row and column keys, and the data values are generic byte data.

Have a look at this piece of documentation: https://docs.janusgraph.org/advanced-topics/data-model/    

Possibly the simplest way to understand the "minimum contract" required by Janusgraph from a backend is to look at the inmemory backend. You will see that:  
- KeyColumnValueStoreManager is conceptually a Map of store name ->  KeyColumnValueStore, 
- each  KeyColumnValueStore is conceptually a NavigableMap of "rows" or KeyValueStores (i.e. a "table") ,
- each KeyValueStore is conceptually an ordered collection of key -> value pairs ("columns").

In the most basic case, once you implement these three relatively simple interfaces, Janusgraph can take care of all the translation of graph operations such as adding vertices and edges, and of gremlin queries, into a series of read-write operations over a collection of KCV stores. When you open a new graph, JanusGraph asks the KeyColumnValueStoreManager implementation to create a number of specially named KeyColumnValueStores, which it uses to store vertices, edges, and various indices. It creates a number of "utility" stores which it uses internally for locking, id management etc.

Crucially, whatever stores Janusgraph creates in your backend implementation, and whatever it is using them for, you only need to make sure that you implement those basic interfaces which allow to store arbitrary byte data and access it by arbitrary byte keys.

So for your first "naive" implementation, you most probably shouldn't worry too much about translation of graph model to KCVS model and back - this is what Janusgraph itself is mostly about anyway. Just use StoreFeatures to tell Janusgraph that your backend supports only most basic operations, and concentrate on thinking how to best implement the KCVS interfaces with your underlying database/storage system.

Of course, after that, as you start thinking of supporting better levels of consistency/transaction management across multiple stores, about performance, better utilising native indexing/query mechanisms, separate indexing backends, support for distributed backend model etc etc - you will find that there is more to it, and this is where you can gain further insights from the documentation, existing backend sources and asking more specific questions.

See for example this piece of documentation: https://docs.janusgraph.org/advanced-topics/eventual-consistency/

Hope this helps,
Dmitry

On Thu, 24 Oct 2019 at 21:27, Debasish Kanhar <d.k...@gmail.com> wrote:
I know that JanusGraph needs a column-family type nosql database as storage backend, and hence that is why we have Scylla, Cassandra, HBase etc. SnowFlake isn't a column family database, but it has a column data type which can store any sort of data. So we can store complete JSON Oriented Column family data here after massaging / pre-processing the data. Is that a practical thought? Is is practical enough to implement?

If it is practical enough to implement, what needs to be done? I'm going through the source code, and I'm basing my ideas based on my understanding from janusgraph-cassandra and janusgraph-berkley projects. Please correct me if I'm wrong in my understanding.

  1. We need to have a StoreManager class like HBaseStoreManager, AbstractCassandraStoreManager, BerkeleyJEStoreManager which extends either DistributedStoreManager or LocalStoreManagerand implements KeyColumnValueStoreManager class right? These class needs to have build features object which is more or less like storage connection configuration. They need to have a beginTransaction method which creates the actual connection to corresponding storage backend. Is that correct?
  2. You will need to have corresponding Transaction classes which create the transaction to corresponding backend like *CassandraTransaction* or *BerkeleyJETx*. The transaction class needs to extend AbstractStoreTransaction` class. Though I can see and understand the transaction being created in BerkeleyJETx I don't see something similar for CassandraTransaction. So am I missing something in my undesrtanding here?
  3. You need to have KeyColumnValueStore class for backend. Like *AsyntaxKeyColumnValueStore* or *BerkeleyJEKeyValueStore* etc. They need to extend KeyColumnValueStore . This class takes care of massaging the data into KeyColumnFormat so that they can then be inserted into corresponding table inside Storage Backend.
    1. So question to my mind are, what will be structure of those classes?
    2. Are there some methods which needs to be present always like I see getSlice() being used across in all classes. Also, how do they work?
    3. Do they just convert incoming gremlin queries into KeyColumnValue structure?
    4. Are there any other classes I'm missing out on or these 3 are the only ones needed to be modified to create a new storage backend?
    5. Also, if these 3 are only classes needed, and let's say we success in using SnowFlake as storage backend, how do the read aspect of janusgraph/query aspect gets solved? Are there any changes needed as well on that end or JanusGraph is so abstracted that it can now start picking up from new source?
  4. And, I thought there would be some classes which would be reading in from "gremlin queries" doing certain "pre-processing into certain data structures (tabular)" and then pushed it through some connection into respective backends. This is where we cant help, is there a way to visualize those objects after "pre-processing"  and then store those objects as it is in SnowFlake and reuse it to fulfill gremlin queries.

I know we can store random objects in SnowFlake, just looking at changed needed at JanusGraph level to achieve those.

Any help will be really appreciated.

Thanks in Advance.

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Ryan Stauffer

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Nov 27, 2019, 10:10:52 AM11/27/19
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Debasish,

This sounds like an interesting project, but I do have a question about your choice of Snowflake.  If I missed your response to this in the email chain, I apologize, but what problems with the existing high-performance backends (Scylla, for instance) are you trying to solve with Snowflake?  The answer to that would probably inform your specific implementation over Snowflake.

Thanks,
Ryan


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Debasish Kanhar

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Nov 28, 2019, 4:40:43 AM11/28/19
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Hi Ryan.

Well that's a very valid question you asked. The current implementation of backends like Scylla as you mentioned are really highly performant. There is no specific problem in mind, but off late I have been dealing with a lot of clients who are migrating their whole system into SnowFlake, including the whole Data storage and Analytics components as well. SnowFlake is a hot upcoming Data storage and warehousing system.

Those clients are really reluctant to add another storage component to their application. Reasons can be a lot like due to high costs, or added complexity of their architecture, or duplication of data across storages. But at the same time these clients also want to incorporate Graph Databases and Graph Analytics into their application as well. This integration is targeted for those set of customers/clients who are/have migrating/migrated into SnowFlake and want to have Graph based component as well. For now, its simply not possible for them to have JanusGraph with their SnowFlake data storages.

Hope I was able to explain it clearly :-)

On Wednesday, 27 November 2019 20:40:52 UTC+5:30, Ryan Stauffer wrote:
Debasish,

This sounds like an interesting project, but I do have a question about your choice of Snowflake.  If I missed your response to this in the email chain, I apologize, but what problems with the existing high-performance backends (Scylla, for instance) are you trying to solve with Snowflake?  The answer to that would probably inform your specific implementation over Snowflake.

Thanks,
Ryan


Evgeniy Ignatiev

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Nov 28, 2019, 5:46:27 AM11/28/19
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Hi.

Is this backend open-source/will be open-sourced?

Best regards,
Evgeniy Ignatiev.

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Debasish Kanhar

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Nov 28, 2019, 10:35:09 AM11/28/19
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Hi Evgeniy,

Thanks for the question. We plan to open source it once implemented but we are still long way from implementation. Will be really grateful to community who can help in any way to achieve this :-)

Debasish Kanhar

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Dec 1, 2019, 4:04:56 AM12/1/19
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Hello any developers following this thread:

As suggested by Dimitry, CQL adopter uses prepared statements, and hence that would be appropriate for me in sense that, I'll be using SQL statements (SnowSQL) for SnowFlake querying using a DAO. Thus CQL and SnowFlake adopter I'm building would be similar and hence makes sense to reference out of those.

As mentioned before, I'm currently blocked at the method getSlice. I know that the method is used while querying the data, but I'm unable to get my head around how does it work internally. A blind implementation might work, but it won't give me an understanding how its working internally. If anyone can help me understand how it works, a similar implementation for SnowFlake becomes easier then.

As mentioned before I'm basing my understanding from CQL adopter. If we look at CQLKeyColumnValueStore under getSlice method, it makes use of this.getSlice prepared statement to fulfill query. The this.getSlice is as follows:

this.getSlice = this.session.prepare(select()
.column(COLUMN_COLUMN_NAME)
.column(VALUE_COLUMN_NAME)
.fcall(WRITETIME_FUNCTION_NAME, column(VALUE_COLUMN_NAME)).as(WRITETIME_COLUMN_NAME)
.fcall(TTL_FUNCTION_NAME, column(VALUE_COLUMN_NAME)).as(TTL_COLUMN_NAME)
.from(this.storeManager.getKeyspaceName(), this.tableName)
.where(eq(KEY_COLUMN_NAME, bindMarker(KEY_BINDING)))
.and(gte(COLUMN_COLUMN_NAME, bindMarker(SLICE_START_BINDING)))
.and(lt(COLUMN_COLUMN_NAME, bindMarker(SLICE_END_BINDING)))
.limit(bindMarker(LIMIT_BINDING)));

The this.getSlice() is used in the method public EntryList getSlice()   which uses the prepared statement above to execute some query. When the following happens (Contents of getSlice method)

final Future<EntryList> result = Future.fromJavaFuture(
this.executorService,
this.session.executeAsync(this.getSlice.bind()
.setBytes(KEY_BINDING, query.getKey().asByteBuffer())
.setBytes(SLICE_START_BINDING, query.getSliceStart().asByteBuffer())
.setBytes(SLICE_END_BINDING, query.getSliceEnd().asByteBuffer())
.setInt(LIMIT_BINDING, query.getLimit())
.setConsistencyLevel(getTransaction(txh).getReadConsistencyLevel())))
.map(resultSet -> fromResultSet(resultSet, this.getter));
interruptibleWait(result);

Is following understanding correct? Anyone with JanusGraph and Cassandra expertise can help.

I'm updating the base query from following bindings:

.where(eq(KEY_COLUMN_NAME, query.getKey().asByteBuffer()))
.and(gte(COLUMN_COLUMN_NAME, query.getSliceStart().asByteBuffer()))
.and(lt(COLUMN_COLUMN_NAME, query.getSliceEnd().asByteBuffer()))
.limit(query.getLimit()));

Is above interpolation correct?

So, if we were to model this in any RDBMS (SnowFlake for eg though SnowFlake isn't RDBMS, it is similar in terms of storage and query engine) with 3 columns as (key, value, column1) of datatypes string (varchar with binary info) can something similar query be correct?

SELECT .... FROM keyspace WHERE
key = query.getKey().asByteBuffer() and
column1 >= query.getSliceStart().asByteBuffer() and
column1 < query.getSliceEnd().asByteBuffer()
limit query.getLimit()

Does this sort of query sound similar in terms of what is targeted to achieve? If I can understand the actual meaning of the prepared statements here, I can also base my undertandings for rest of methods which would be required for doing mutations in underlaying backend.

Any help is really appreciated as we are kinda getting tighter and tighter on deadline regarding the feasibility PoC of SnowFlake as backend for JanusGraph.

Thanks in advance

Dmitry Kovalev

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Dec 2, 2019, 7:26:58 PM12/2/19
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Hi Debashish,

in terms of wrapping one's head around what getSlice() method does - conceptually it is not hard to understand, if you peruse the link I have referred you to in my original reply:

The relevant part of it is really short so I'll just copy it here (with added emphasis in bold):
===quote===

Bigtable Data Model

Under the Bigtable data model each table is a collection of rows. Each row is uniquely identified by a key. Each row is comprised of an arbitrary (large, but limited) number of cells. A cell is composed of a column and value. A cell is uniquely identified by a column within a given row. Rows in the Bigtable model are called "wide rows" because they support a large number of cells and the columns of those cells don’t have to be defined up front as is required in relational databases.

JanusGraph has an additional requirement for the Bigtable data model: The cells must be sorted by their columns and a subset of the cells specified by a column range must be efficiently retrievable (e.g. by using index structures, skip lists, or binary search).

===/quote===

Basically, getSlice method is the formal representation of above requirement in bold:  based on the order defined for "column keys" space, it should return all "columns" whose keys lay "between" a start and end key values, given in SliceQuery... that is, >= start and <=end... Please refer to the javadoc for more detail.


However, answering the question of how do you effectively implement it in your backend is pretty much the crux of your potential contribution.

If the underlying DB's data model more or less "natively" supports the above (as e.g. in the case of Cassandra, BDB etc), then it becomes relatively easy.

If the underlying data model is different, then it gets us back to the question which has been asked a couple of times in this thread - i.e. whether it is actually feasible and/or desirable to try and implement it?

For example, in order to implement it in a "classical" RDBMS, your would have to find one which supports ordering and indexing of byte columns/blobs, and then probably encounter scalability issues if you chose to model the whole key-column-value store as one table with row key, column key and data... It might still be possible to address these issues and implement it reasonably effectively, but it is unclear what would be the point - as you would effectively have to circumvent the "relational/SQL" top abstraction layer, which is the whole point of RDBMS, to get back to lower level implementation details.

Unfortunately I know nothing about Snowflake and it's data model, and don't have the time to learn about it in any sufficient detail any time soon, so I cannot really advise you neither on feasibility nor on any implementation details.

Hope this helps,

Dmitry

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Dmitry Kovalev

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Dec 2, 2019, 8:32:48 PM12/2/19
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A few more things which you might find helpful:

1) To help you verify if your implementation is correct, you can utilise the standard test suite which is used to test the correctness of all backends - more or less all you need to do is extend KeyColumnValueStoreTest and override the setup methods to provide an instance of your store implementation. See e.g. CQLStoreTest

2) If you plan to opensource your work anyway, it may help if you make your work in progress public - e.g. put it on Github or Gitlab etc right now. This way you can refer to specific code, and may even get someone to help out. Of course it is not always possible depending on your company's policies, but if it is - it may be beneficial.

Debasish Kanhar

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Dec 4, 2019, 12:06:08 AM12/4/19
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Thanks Dimitry for the detailed explanation.

Few of my counter questions:

I had gone through the the Big Data model you mentioned and also the architecture diagram of underlaying Titan Blueprints Graph (Some 6 year old repo). I was able to deduce the internal structure how Janus stores the intrinsic Graph elements. It stores as Adjacency list as shown in image you shared where the key is "Row Key for Vertex. Maybe sereliazed version of its vertex ID or unique identifier? ". The row of vertex has 2 components within it except for RowKey. i.e.
1: All unique properites/relations. It in turn contain column within it storing meta information for the relation. This is also sorted by "ColumnKey" which is probably combination of RelationName and some ID.
2: All non unique relations. It is as super column under which we have multiple columns, sorted by "ColumnKey" and retrivable according to that as well.

And, I think these above 2 types of relations are the ones which are queries / retrived from Janus using getSlice method. Is that correct?

But then when I tried to model this as is, I though we would have columns corresponding to each relation/relation super column.But to verify my understanding I did query on internal table structure in Cassandra to understand the structurr, and as mentioned I just saw 3 columns not "N" columns corresponding to each relation I was expecting.

If we are to map those column to the data structure defined above, how do they map?
Key is same as RowKey
value is same as collection of unique relations?
column1 is collection of all super columns?

If the above is correct, it helps a lot in understanding getSlice method.

But then it brings me to next question:
Whenever a row is inserted, it means that either a new vertex is added, or existing vertex is mutated in some way or other. So, based on above understanding, "value" as "serialized format" remains the same. So does its "column1". As the represent some static information regarding a vertex. i.e. its relations and properties. So, whenever you do, "getSlice between sliceStart and sliceEnd", the results won't change unless sliceStart and sliceEnd conditions change. Is that understanding correct as well?

So, is this understanding correct as well: Fetch a row first. Then fetch its subset of properties if and only if they fall under a range of sliceStart and sliceEnd?

Also, you don't need to think this from SnowFlake perspective but think of this from RDBMS perspective. Anything possible in RDBMS is possble in SnowFlake in additon to extra features. So if its possible in RDBMS its logically possible in SnowFlake as well.

Really thanks again for your suggestions. If you can clear a few counter doubts, w.r.t. any RDBMS, that will be great.

But looks like only way to check feasibility study would be to implement Unit tests (My implementation of CQLStoreTest). Is that correct?


On Tuesday, 3 December 2019 05:56:58 UTC+5:30, Dmitry Kovalev wrote:
Hi Debashish,

in terms of wrapping one's head around what getSlice() method does - conceptually it is not hard to understand, if you peruse the link I have referred you to in my original reply:

The relevant part of it is really short so I'll just copy it here (with added emphasis in bold):
===quote===

Bigtable Data Model

Under the Bigtable data model each table is a collection of rows. Each row is uniquely identified by a key. Each row is comprised of an arbitrary (large, but limited) number of cells. A cell is composed of a column and value. A cell is uniquely identified by a column within a given row. Rows in the Bigtable model are called "wide rows" because they support a large number of cells and the columns of those cells don’t have to be defined up front as is required in relational databases.

JanusGraph has an additional requirement for the Bigtable data model: The cells must be sorted by their columns and a subset of the cells specified by a column range must be efficiently retrievable (e.g. by using index structures, skip lists, or binary search).

===/quote===

Basically, getSlice method is the formal representation of above requirement in bold:  based on the order defined for "column keys" space, it should return all "columns" whose keys lay "between" a start and end key values, given in SliceQuery... that is, >= start and <=end... Please refer to the javadoc for more detail.


However, answering the question of how do you effectively implement it in your backend is pretty much the crux of your potential contribution.

If the underlying DB's data model more or less "natively" supports the above (as e.g. in the case of Cassandra, BDB etc), then it becomes relatively easy.

If the underlying data model is different, then it gets us back to the question which has been asked a couple of times in this thread - i.e. whether it is actually feasible and/or desirable to try and implement it?

For example, in order to implement it in a "classical" RDBMS, your would have to find one which supports ordering and indexing of byte columns/blobs, and then probably encounter scalability issues if you chose to model the whole key-column-value store as one table with row key, column key and data... It might still be possible to address these issues and implement it reasonably effectively, but it is unclear what would be the point - as you would effectively have to circumvent the "relational/SQL" top abstraction layer, which is the whole point of RDBMS, to get back to lower level implementation details.

Unfortunately I know nothing about Snowflake and it's data model, and don't have the time to learn about it in any sufficient detail any time soon, so I cannot really advise you neither on feasibility nor on any implementation details.

Hope this helps,

Dmitry

Debasish Kanhar

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Feb 3, 2020, 3:40:55 PM2/3/20
to JanusGraph developers
To anyone if they are following this Thread. Wanted to post an update if anyone is interested, else will close out the Thread.

So, We were able to get the adopter working for SnowFlake. We planned on open sourcing it, and for now its hosted on Gitlab (https://gitlab.com/system-soft-technologies-opensource/janus-snowflake) if anyone is interested to take a look.

The storage adopted we created tries to model SnowFlake as KeyValueStore, it can be modelled as KeyColumnValueStore as well, but its all about deciding about underlaying data structure and doing required transformations.

But, as suspected, we see dredful drop in performance. Since JanusGraph issues various multi part queries, that kind of slows  down the process overall. To be honest, we aren't able to do any sort of WRITE operation in practical enough time, and are only able to do READ operation with slower response (almost on border line of what can be thought to be acceptable). To tackle the issue of WRITE opearation, we are implementing a custom write pipeline where we fetch data from input tables, transform it and load to local BerkleyDB store. We then iterate over BerkleyDB local files/tables and load those in SnowFlake. Our gremlin server can then pick up from the set of SnowFlake tables to serve any sort of Gremlin queries for READ operation.

Evgeniy Ignatiev

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Feb 4, 2020, 6:12:09 AM2/4/20
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Hello.

Awesome job! I have a couple of questions about your data loading approach if you don't mind.

Is it simply aggregating writes locally before writing them to Snowflake? Or do you also use BerkeleyDB as a local write-through cache, from where reads are served for data is not yet in Snowflake?

Drop in performance sounds expectable in comparison to Cassandra, it is not simply RDBMS vs NoSQL, but DWH vs NoSQL, Snowflake is really not optimized to perform multiple small operations, single insert is almost of the same latency as bulk insert, ideally significantly large bulk insert for JDBC driver to leverage internal stage loading optimization, as I understand you are going to do it manually through PUT FILE + COPY INTO combination.  Updates are significantly slower and single updates are really devastating to performance (order of magnitude degradation with hundreds of concurrent threads) due to locking behavior and write amplification that Snowflake micro-partitioning should perform (overwriting whole micro-partition and/or creating single record file which will result in single object stored in underlying storage like S3).

Also bulk reading by means of SQL might not be worth it too, e.g. if you want to use SparkGraphComputer - Snowflake Spark connector itself, issues direct SQL queries only to request metadata, even for native SQL backed DataFrames/DataSets. Actual reading happens in parallel from executors by offloading data to S3 stage and reading directly from it.

Best regards,
Evgeniy Ignatiev.

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Best regards,
Evgeniy Ignatiev.

Debasish Kanhar

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Apr 6, 2020, 12:12:27 PM4/6/20
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Hi Evgeniy Ignatiev.

Sorry about late response. Might have missed out the message. Was really busy with trying all sorts of possible explorations to make SnowFlake + JanusGraph faster, but not much success.
Well yes, we are using BerkleyDB as some sort of local write-through cache. That seems only way we can have acceptable level of performance in the system.

During data loading ,we load the data into BerkleyDB which is cached/backed up at regular intervals. Once the specified time is elapsed, we take backup/copy of local BerkleyDB storage, then do bulk
Migration by iterating through BerkleyDB records, creating custom SQL queries and load that to SnowFlake then create another new BerkleyDB for new time range.

Such way, we are able to do data writes at more faster rate, and we also make use of the local version of backued up BerkleyDB to server Read requests as well thus helping us save time.

The only issue with this approach is that, the Graphs across time intervals of backup are disconnected. i.e. let's say I took backup in BerkleyDB w.r.t 05-05-2020 and another on 06-04-2020, so the Graphs for same node will be different based on the request date.
Since our use case requires us to view Graphs only across a specified time period, and not across universal time period, so we don't care for that as of now, but I feel this might be an important issue if above mentioned solution is made a generic solution.
One possible alternative to handle this  each time we create a new local BerkleyDB after specified time window is crossed, we can create another background app which can append to our BerkleyDB store, such that one Global BerkleyDB store keeps on increasing in size and becomes the de facto
local store to serve all requests for all dates and helps us build an universal Graph for a node. But don't know how practical this solution is.


Snowflake is really not optimized to perform multiple small operations, single insert is almost of the same latency as bulk insert
This is turning out to be bigges challenge as you mentioned. We got in call with Co-founder of Snowflake, and they are now looking at implementing Prepared statements for Snowflake which is missing. I'm being told by him that once Prepared statements are done, the repeated queries can be optimized by 70-90%
and we need exactly that, as the Snowflake queries are repetitive, except that it changes only in Key range. But such implementation is arelast 1 year away as he mentioned.

Updates are significantly slower and single updates are really devastating to performance
I know, but per my understanding there is no updates. We only do WRITE query, which we do in bulk while migrating from Snowflake. Our use case don't need any writes on the fly, so haven't explored how the corresponding Snowflake queries are forumalated, but I still didn't see any UPDATE queries may it be in CQL or BerkleyDB. As for READs, its only select statements which are executed against Snowflake in our case.

Updates are significantly slower and single updates are really devastating to performance
Oh, you brought out a really nice point. We are planning to implement a bulk read and write, so that we can bulkify the repeatative queries we do to Snowflake w.r.t single operation from Snowflake, like Querying for index is iterative process, we can bulkify that. Or querying for edges of a single vertex is iterative process which we can bulkify. So if we want to do query for 5 vertices, it becomes 5 bulked queries. On those lines. But we will have to change the core code of Janusgraph, Tinkerpop so that bulked queries can be reconciled to form single Graph object. We have started exploration into that, and I'll be creating a write up for those in Janusgraph-dev and Gremlin-users groups, asking anyone from community who can help in those aspects. Its a long process, but making Snowflake work with JanusGraph is proving out to be more challenging. :-( The reason why we have to stick with Snowflake backend is because the whole application has migrated to Snowflake, and we don't know what to do with our Graph component, as I don't know any Graph applicaion which works on top of Snowflake

Hope you check out my other post on my last point I mentioned, and hope for some comments from you :-)
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