The other two servers had pure MySQL workload. Also, the updates needed to be propagated. So there is the deadlock. I searched around to find nothing useful, but I remembered there is a cron called incrond which can watch files and directories for events using INOTIFY and execute commands when specific events occur. The solution is almost there. All I need is a script to copy the database file to other servers when data was written to it.
The data is simply marked for deletion and reused during future inserts.
Nevertheless, since the data size was pretty small, I used scp to transfer the database. Whenever the file is modified, it will be transferred to the other servers.
Using the SQLite Online Backup API
In the sense, the program could see the deleted row. This is mainly because of caching in memory. So I just added the commands for reloading the program in the script before syncing the database to other servers on the primary server and then two ssh commands in the script which execute the reload command on the other two servers.
January 4, at AM. Has anyone actually tried the rsync incremental updates? We would like to port this for an android app used by small shops in Dakar.
January 4, at PM. Thank you so much for your quick reply Nilesh. So we start today using it. Would you be interested in following developments of rsync integration? Any email address or Telegram number I could reach out to you? If you have anything that will be useful to someone else looking for it please post it as a comment. You can ping me on twitter : nileshgr.
November 18, at AM. November 18, at PM. July 4, at PM. That would also allow you to handle replication both ways : if the database was changed on both sides, the changes can be merged. May 20, at PM. April 18, at AM. I was going to setup a ghost website with a SQLlite database backend distributed across 3 nodes, but i was thinking of using lsyncd for the replication since lsyncd incorporates both the inode watching and rsync functions.SymmetricDS 3.
Along with. Here are some highlights:. Download SymmetricDS 3. See the 3. This release includes 6 new features and 9 improvements. Enhanced common batch mode to always be enabled Queuing of initial load in background, separated from routing Support for extract-only nodes without runtime tables Support for SAP HANA database as a target Reduced size of data events for improved routing performance Faster purge service, even when nodes are offline Improved authentication with temporary security token in header.
This release includes 14 bug fixes and 12 improvements. Here are some issues to highlight:. Load testing of database replication finds the upper limit of how well the system can perform, and it provides assurance that replication will make it through times of peek usage. Let's look at how to simulate production activity for SymmetricDS data replication in a lower environment so you can deploy with confidence. All rights reserved. Add a comment.
Here are some highlights: Enhanced common batch mode to always be enabled Queuing of initial load in background, separated from routing Support for extract-only nodes without runtime tables Support for SAP HANA database as a target Reduced size of data events for improved routing performance Faster purge service, even when nodes are offline Improved authentication with temporary security token in header Download SymmetricDS 3.
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rqlite v3: Globally replicating SQLite
Sign up. With this framework your application can work completely offline Airplane Modethen perform an automated Bidirectional Synchronization when an internet connection becomes available. Java Branch: master. Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Latest commit 2be Feb 24, The time has come for mobile app developers to accept reality. You signed in with another tab or window.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. In an application which embeds SQLite3 and uses an in-memory database, is it possible to replicate the database between two running instances of the application?
I could do this by hand with a homebrew protocol duplicating all my DB accesses, but it seems like something that should be done inside the DB layer. Brute force approach: Send it the ". Read that data in into the second database. Not sure you can use that. But how do you plan to handle errors? For example, what happens when the copy of the DB in app2 can't make an update for some reason? I haven't tried it yet.
Seems to have been around a bit. Pretty new, but an evolution of Litereplica so probably more mature than it appears. I have tried this a bit and it does seem to work smoothly, with a few bugs which the developer is looking at. You have to use the developer's modified SQLite engine, which seems like a concerning dependency.
You also don't get much control, e. Lsyncd - Live Syncing Mirror Daemon may be of use here. It uses rsync to do continuous replication on the file level. No it doesn't because the project's scope is being a simple in-process database. But because the database is just a single file, you could write your own replication script based on plain file copy operations, rsync or something similar.
Best you could do though was hot spare, because SQLite db in one monolithic file. You couldn't round-robin between the two "instances". But with unison you have master-master. Learn more. Does SQLite support replication?
Ask Question. Asked 10 years, 4 months ago. Active 10 months ago. Viewed 23k times.About Documentation Download Support Purchase. Search Documentation Search Changelog. Copy the database file using an external tool for example the unix 'cp' utility or the DOS 'copy' command. Relinquish the shared lock on the database file obtained in step 1. This procedure works well in many scenarios and is usually very fast. However, this technique has the following shortcomings: Any database clients wishing to write to the database file while a backup is being created must wait until the shared lock is relinquished.
It cannot be used to copy data to or from in-memory databases.
If a power failure or operating system failure occurs while copying the database file the backup database may be corrupted following system recovery. The online backup API allows the contents of one database to be copied into another database, overwriting the original contents of the target database. The copy operation may be done incrementally, in which case the source database does not need to be locked for the duration of the copy, only for the brief periods of time when it is actually being read from.
This allows other database users to continue uninterrupted while a backup of an online database is made. The online backup API is documented here. The remainder of this page contains two C language examples illustrating common uses of the API and discussions thereof.
Reading these examples is no substitute for reading the API documentation! Error handling If an error occurs in any of the three main backup API routines then the error code and message are attached to the destination database connection. This feature is used in the example code to reduce amount of error handling required.
Since database zFilename is a file on disk, then it may be accessed externally by another process. Usually, it does not matter if the page-sizes of the source database and the destination database are different before the contents of the destination are overwritten.
The page-size of the destination database is simply changed as part of the backup operation. The exception is if the destination database happens to be an in-memory database. Unfortunately, this could occur when loading a database image from a file into an in-memory database using function loadOrSaveDb.
Function loadOrSaveDb could detect this case, and attempt to set the page-size of the in-memory database to the page-size of database zFilename before invoking the online backup API functions. This requires holding a read-lock on the source database file for the duration of the operation, preventing any other database user from writing to the database. It also holds the mutex associated with database pInMemory throughout the copy, preventing any other thread from using it. File and Database Connection Locking During the ms sleep in step 3 above, no read-lock is held on the database file and the mutex associated with pDb is not held.
This allows other threads to use database connection pDb and other connections to write to the underlying database file.
There is one exception to this rule: If the source database is not an in-memory database, and the write is performed from within the same process as the backup operation and uses the same database handle pDbthen the destination database the one opened using connection pFile is automatically updated along with the source. Whether or not the backup process is restarted as a result of writes to the source database mid-backup, the user can be sure that when the backup operation is completed the backup database contains a consistent and up-to-date snapshot of the original.
However: Writes to an in-memory source database, or writes to a file-based source database by an external process or thread using a database connection other than pDb are significantly more expensive than writes made to a file-based source database using pDb as the entire backup operation must be restarted in the former two cases.
If the backup process is restarted frequently enough it may never run to completion and the backupDb function may never return.
This is not usually a problem.Your application will use a modified version of the SQLite library containing the LiteSync code to access your database. The first time the app is open it will connect to the other node s and download a fresh copy of the database.
In a centralized topology the primary node will send the database copy to the secondary nodes. Once the nodes have the same base db they exchange transactions that were executed when they were off-line. After this they enter in on-line mode and once a new transaction is executed in a node it is transferred to be executed in the connected nodes.
If the node is off-line then the transaction is stored in a local log to be exchanged later. There are a few steps but basically we must change the URI string in the database opening from this:. It means that we don't need to use another API. So you can choose which side will connect to the other. This is useful when one side is behind a router or firewall. In this topology we have a node in which all the other nodes will be connected to, so it must be on-line for the synchronization to take place.
If the app is being open for the first time on a device it can download a new copy of the database from another node. Until it is done we cannot access the db. For other languages you must have the proper wrapper installed. The primary node can be a normal application, exactly the same app as the secondary nodes but using a different URI.
A basic standalone application used solely for the purpose of keeping a centralized db node would look like this:. Connection; import java. Data; using System. Imports System. Data Imports System. Open ' keep the app open Do System. DriverManager; import java. ResultSet; import java. Statement; import org.
SQLite; using System. DeserializeObject string command. SQLite Imports System. DeserializeObject Cmd. ExecuteScalar If status! Recordset Rst. Close rows. No old journal mode. Do not let many apps access the same database file.It gracefully handles leader election, and can tolerate machine failure. With the v3 release seriesrqlite can now replicate SQLite databases on a global scale, with very little effort. The EC2 system makes it simple to fire up a global presence, so I did just that.
I launched 3 m4. For the purposes of this experiment, I made the Security Groups wide open, so there would be no problems with network access. The source of this script is available here. So I ran the following commands on the EC2 instance in Oregon. We now have a single rqlite node, with a real SQLite database underneath it. To do that I run the next commands on each of the two remaining EC2 instances:. The new table and row have been replicated to the two new nodes. And, of course, every future change made on the leader SQLite database will be replicated synchronously to the other 2 nodes, placed out of harms way, thousands of miles from the leader.
This 3-node cluster can tolerate the failure of a node, and if that node is the leader, a new leader will be elected within a couple of seconds. If the cluster was 5 nodes in size, it could tolerate the failure of two nodes. This API will also redirect clients to the leader node, if the node contacted is not the leader.
You can connect the CLI to any node, and it will transparently redirect to the leader automatically, if necessary. Good post and good project.
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Check the network To get an idea of network latency, I ran some ping tests. From Oregon to Dublin. PING Is this cluster practical? Probably not on a network with such high latency between the nodes. In this set up I managed to insert about 2 rows a second, though if transactions and bulk updates are used, the effective rate is much higher.
Running a cluster on a global scale is mostly for demonstration purposes, and to drive development of rqlite forward to the point where it was technically possible to replicate at this scale.
However, within, say, a single EC2 Region, the performance will be much greater. And by running an rqlite cluster within the same data-center, with each node on a different rack for reliability, one should see s of insertions a second. And all with very easy deployment and operation. The code for rqlite is open-source and is available on GitHubas are pre-built releases. Previous Post rqlite v3.
Hi Jean — I am not specifically aware of any such projects. Leave a Reply Cancel reply Your email address will not be published. Philip O'Toole.