i want to implement a feature that shows when a couchbase document is last read.
Is this saved by default in meta data of couchbase or i need to update the document with a field on every read so it can be retrieved later on .
There's nothing like that in the metadata, you'd have to update the document yourself.
Side note: For writes/updates, you could have made use of the auditing annotation feature of Spring Data (supported by Spring Data Couchbase since SDC 2.1.1) but not for reads.
Also note that performance will suffer as you'd have to effectively perform a write for each read. And there's also the potential consistency side-effects: what if there's already a write of the same document happening in parallel?
To implement this, if you can wait for Couchbase Server 4.5, you should maybe consider using the sub-document API. (see this blog).
Related
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).
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)
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.
I am trying to sync pouchDB with couchBase through Sync Gateway, but i just get data added by pouchDB, not initial data added to couchBase. For example there is 750 docs in couchBase but none of them synced to the pouchDB. Also http://localhost:4985/_admin/db/db not showing couchBase docs too.
The problem is with adding data to Couchbase Server directly. Couchbase Mobile currently requires extra metadata in order to deal with replication and conflict resolution. This isn't handled by the Server SDKs.
The recommended approach is to do all database writes through Sync Gateway.
To simplify use with PHP, you may want to use a Swagger PHP client. (You can see an example of using clients autogenerated by Swagger in this post. The example use Javascript and Node.js, but the principles are the same.)
You can read from Couchbase Server directly if you want (to do a N1QL query, for example).
Another option is to use "bucket shadowing". This is trickier, and is likely to get deprecated at some point. I only list it for completeness.
I am working on a project that uses Couchbase Server and Sync Gateway to synchronize the contents of a bucket with iOS and Android clients running Couchbase Lite. I also need read and write access to the Couchbase Server from a Node.js server application. From the research I've done, using shadowing is frowned upon (https://github.com/couchbase/sync_gateway/wiki/Bucket-Shadowing), which led me to look into the Sync Gateway API as a means to update the bucket from the Node.js application. Updating existing documents through the Sync Gateway API appears to require the most recent revision ID of the document to be passed in, requiring a separate read before the modification (http://mobile-couchbase.narkive.com/HT2kvBP0/cblite-sync-gateway-couchbase-server), which seems potentially inefficient. What is the best way to solve this problem?
Updating a document (which is really creating a new revision) requires the revision ID. Otherwise Couchbase can't associate the update with a parent. This breaks the whole approach to conflict resolution. (Couchbase uses a method known as multiversion concurrency control.)
The expectation is that you're updating the existing contents of a document. This implies you've read the document already, including the revision ID.
If for some reason you don't need to the old contents to update the document, you still need the revision ID. If you work around it (for example, by purging a document through Sync Gateway and then pushing your new version) you can end up with two versions of document in the system with no connection, which will cause a special kind of conflict.
So the short answer is no, there's no way to avoid this (without causing yourself other headaches).
I am not sure why your question was downvoted, as it seems like a reasonable question. You are correct, the Couchbase bucket that is used by Sync Gateway should probably best be thought of as "opaque", you should not be poking around in there and changing things. There are a number of implementations of Couchbase Lite, such as one for Java, .NET, and Mac OS X. Have you considered making a web service that, on one side, is serving your application, and on the other side is itself a Couchbase Lite client? You should be able to separate your data as necessary using channels.
I am designing a high volume service which essentially works as a token creation and validation service. Today we use SQL based databases which are fast failing to scale and the alternative that we are looking at is Couchbase server (memcached). However, the use case is the token generated by this service is sent to other services where the token will be used for authentication. If the replication is not fast enough, the authentication fails. Is there a simpler means to achieve this either via code or any other alternatives is also welcome. This seems to us to be a "read-your-own-write" use case.
There is no consistency API for XDCR right now. It's probably somewhere on the dev roadmap, because it's one of the commonly requested features.
If you want to get RYOW consistency across data centers, our only option is to write to all the DCs simulataneously from the application code. Of course, it's not atomic, but you can work around that somewhat by waiting for all the clusters to acknowledge the write before proceeding.
I think you might be misunderstanding what replication is for in Couchbase. Couchbase is strongly consistent for standard data operations. If you write a document or key/value pair, you can immediately read that object. No waiting for replication. The use case you are talking about is a very common one for Couchbase.
The only things that are eventually consistent in Couchbase are XDCR, for obvious reasons, and reading from views. Even then, this can be minimized with proper cluster sizing.
am I correct assuming that if a different process updates the DB then my NHibernate powered application will be out-of-sync? I'm almost using non-lazy update.
My target DB is mysql 5.0, if it makes any difference.
There isn't a simple way to answer that without more context.
What type of application are you thinking about (web, desktop, other)?
What do you think would be out of sync exactly?
If you have a desktop application with an open window with an open session that has data loaded and you change the same entities somewhere else, of course the DB will be out of sync, but you can use Refresh to update those entities.
If you use NH second-level caching and you modify the cached entities somewhere else, the cache contents will be out of sync, but you can still use Refresh or cache-controlling methods to update directly from the DB.
In all cases, NH provides support for optimistic concurrency by using Version properties; those prevent modifications to out-of-sync entities.
Yes, the objects in your current session will be out of sync, the same way a DataSet/DataTable would be out of sync if you fetch it and another process updates the same data.