Using Couchbase SDK vs Sync Gateway API

Question

I have a full deployment of couchbase (server, sync gateway and lite) and have an API, mobile app and web app all using it.

It works very well, but I was wondering if there are any advantages to using the Sync Gateway API over the Couchbase SDK? Specifically I would like to know if Sync Gateway would handle larger numbers of operations better than the SDK, perhaps an internal queue/cache system, but can't seem to find definitive documentation for this.

At the moment the API uses the C# Couchbase SDK and we use SyncGateway very little (only really for synchronising the mobile app).

Answer 1

The short answer is that for backend operations, Couchbase SDK is your choice, and will perform much better. Sync Gateway is meant to be used by Mobile clients, with few exceptions (*).

Bulk/Batch operations

In my performance tests using Java Couchbase SDK and bulk operations from AsyncBucket (link), I have updated up to 8 thousand documents per second. In .Net there you can do Batch operations too (link).

Sync Gateway also supports bulk operations, yet it is much slower because it relies on REST API and it requires you to provide a _rev from the previous version of each document you want to update. This will usually result in the backend having to do a GET before doing a PUT. Also, keep in mind that Sync Gateway is not a storage unit. It just works as a proxy to Couchbase, managing mobile client access to segments of data based on the channels registered for each user, and writes all of it's meta-data documents into the Couchbase Server bucket, including channel indexing, user register, document revisions and views.

Querying

Views are indexed thus for querying of large data they may will respond very fast. Whenever a document is changed, the map function of all views has the opportunity to map it. But when a view is created through Sync Gateway REST API, some code is added to your map function to handle user channels/permissions, making it slower than plain code created directly in Couchbase Admin UI. Querying views with compound keys using startKey/endKey parameters is very powerful when you have hierarchical data, but this functionality and the use of reduce function are not available for mobile clients.

N1QL can also be very fast too, when your N1QL query is taking advantage of Couchbase indexes.

Notes

(*) One exception to the rule is when you want to delete a document and have this reflected on mobile phones. The DELETE operation, leaves an empty document with _deleted: true attribute, and can only be done through Sync Gateway. Next time the mobile device synchronizes and finds this hint, it will delete the document from local storage. You can also use set this attribute through a PUT operation, when you may also adding _exp: "2019-12-12T00:00:00.000Z" attribute to perform a programmed purge of the document in a future date, so that the server also gets clean. However, just purging a document through Sync Gateway is equivalent to delete it through Couchbase SDK and this won't reflect on mobile devices.

NOTE: Prior to Sync Gateway 1.5 and Couchbase 5.0, all backend operations had to be done directly in Sync Gateway so that Sync Gateway and mobile clients could detect those changes. This has changed since shared_bucket_access option was introduced. More info here.

Answer 2

First, some relevant background info :

Every document that needs to be synced over to Couchbase Lite(CBL) clients needs to be processed by the Sync Gateway (SGW). This is true whether a doc is written via the SGW API or whether it comes in via server write (N1QL or SDK). The latter case is referred to as "import processing” wherein the document that is written to the bucket (via N1QL) is read by SGW via DCP feed. The document is then processed by SGW and written back to the bucket with the relevant sync metadata.

Prerequisite :

In order for the SGW to import documents written directly via N1QL/SDK, you must enable “shared bucket access” and import processing as discussed here

Non-mobile documents :

If you have documents that are never going to be synced to the CBL clients, then choice is obvious. Use server SDKs or N1QL

Mobile documents (docs to sync to CBL clients) :

Assuming you are on SGW 2.x syncing with CBL 2.x clients

If you have documents written at server end that need to be synced to CBL clients, then consider the following

• Server side write rate:

If you are looking at writes on server side coming in at sustained rates significantly exceeding 1.5K/sec (lets say 5K/sec), then you should go the SGW API route. While it's easy enough to do a bulk update via server N1QL query, remember that SGW still needs to keep up and do the import processing (what's discussed in the background).

Which means, if you are doing high volume updates through the SDK/N1QL, then you will have to rate limit it so the SGW can keep up (do batched updates via SDK)

That said, it is important to consider the fact that if SGW can't keep up with the write throughput on the DCP feed, it's going to result in latency, no matter how the writes are happening (SGW API or N1QL)

If your sustained write rate on server isn’t excepted to be significantly high, then go with N1QL.

• Deletes Handling:

Does not matter. Under shared-bucket-access, deletes coming in via SDK or SGW API will result in a tombstone. Read more about it here

• SGW specific config :

Naturally, if you are dealing with SGW specific config, creating SGW users, roles, then you will use the SGW API for that.

• Conflict Handling :

In 2.x, it does not matter. Conflicts are handled on CBL side.

Challenge with SGW API

• Probably the biggest challenge in a real-world scenario is that using the SG API path means either storing information about SG revision IDs in the external system, or perform every mutation as a read-then-write (since we don't have a way to PUT a document without providing a revision ID)