I'm trying to setup a Fuseki service with a persistent TDB store and an in-memory Lucene index. My configuration works fine. But when I restart Fuseki, the in-memory index is of course lost. Is there any way to rebuild the index without having to reload the data? I know I can use
$ java -cp $FUSEKI_HOME/fuseki-server.jar jena.textindexer --desc=config.ttl
if I had a persistent index, but since it requires Fuseki to be stopped, it doesn't work with an in-memory index.
Related
I have a C application that inserts data directly to the database of my Meteor application. The app works fine (withoud delays) when I run it in development mode (with "meteor"). However, if I run the app as a node app (bundled) and with external MongoDB, there's an annoying delay in screen updates (5-10s).
I have noticed some previous discussions about this:
Meteor: server-side db insert delays
Using node ddp-client to insert into a meteor collection from Node
Questions:
Is there any other way than building a server-side API for doing the db inserts through Meteor?
Why the delay is only when using external MongoDB?
Is there a way in Meteor to shorten this database polling interval?
You need to enable oplog tailing. Without oplog tailing, when your C program makes a database write, the Meteor server doesn't realise anything has changed until it polls MongoDB again. With oplog tailing, it can pick up the changes much more quickly and efficiently. In development mode, oplog tailing is enabled automatically, but for production it needs some additional setup.
Your MongoDB must be set up as a replica set (a replica set of one node does work).
You have to pass in a mongo URL for the replica set's local database with the environment variable MONGO_OPLOG_URL.
For more information, see this article.
I'm a MongoDB beginner.
I'm working on Intellijidea IDE to develop JAVA program in the aim to execute data mining processes on social media like Twitter and Facebook, based on Twitter4j and Facebook4j.
I use MongoDB to store database collections for test and evaluation purposes. I have saved several MongoDB databases, which were all accessible until a few days, in a folder as E:/data/db. So, all my previous databases are accessible in E:/data/db and I can easily control the structure of the databases collections through a terminal command in windows shell (show dbs(), show collections(), db stats()).
Last week, I launched a new data mining database collection, with several collections, and probably made a mistake in the localization of the database on my computer, where I put the new database in E:/data/db/newdatabase.
The problem is that I need to get the data mining process running while I would like to analyze the old databases collections through the R software.
Right now, I'm not able to access to the old MongoDB databases on Windows terminal command, as I can see only that there is some bytes, but no structured collections etc… When I'm trying to call the collections and the databases from R with rmongodb package, I'm not able to see the previous collections.
Might I be able to restore the old databases collections with Mongo restore or something like that ? What Kind of mistake could I have done to keep these old databases collections not accessible while there were a few days ago ?
MongoDB is not intended to be manipulated at the filesystem level.
Instead, you should be using mongoexport and mongoimport to transfer individual databases.
Check if you still have your collections data in your E:\data\db directory, named with your collection name
yourCollection.0
yourCollection.1
yourCollection.ns
Try by copy your newdatabase and db folder in a new folder (like E:\backup) then try to start two mongo instance :
mongod --dbpath=E:\backup\db --port 27001
mongod --dbpath=E:\backup\newdatabase --port 27002
try to connect to each dabase and check if eveything is ok (no data corruption, ...)
mongo --port 27001
mongo --port 27002
If it's ok, then, as jmkgreen explain, export your database, and import it in your previous database.
I'm trying to backup my sqlite database from a cronjob that runs in 5 minute intervals. The database is "live", so there are running queries at the time I want to perform the backup.
I want to be sure, that the database is in good shape when I backup it so that I can rely on the backup.
My current strategy (in pseudocode):
function backup()
{
#try to acquire the lock for 2 seconds, then check the database integrity
sqlite3 mydb.sqlite '.timeout 2000' 'PRAGMA integrity_check;'
if (integrity is ok and database was not locked)
{
#perform the backup to backup.sqlite
sqlite3 mydb.sqlite '.timeout 2000' '.backup backup.sqlite'
if (backup could be performed)
{
#Check the consistency of the backup database
sqlite3 backup.sqlite 'PRAGMA integrity_check;'
if (ok)
{
return true;
}
}
}
return false;
}
Now, there are some problems with my strategy:
If the live database is locked, I run into problems because I cannot perform the backup then. Maybe a transaction could help there?
If something goes wrong between the PRAGMA integrity_check; and the backup, I'm f*cked.
Any ideas? And by the way, what is the difference between the sqlite3 .backup and a good old cp mydb.sqlite mybackup.sqlite ?
[edit] I'm running nodejs on an embedded system, so if someone suggests the sqlite online backup api with some ruby wrapper - no chance ;(
If you want to backup while queries are running you need to use the backup API. The documentation has a worked out example of an online backup of a running database (example 2). I don't understand the Ruby reference, you can integrate it in your program or do it as a small C program running besides the real application -- I've done both.
An explicit integrity_check on the backup is overkill. The backup API guarantees that the destination database is consistent and up-to-date. (The flip side of that coin is that if you update the DB too often while a backup is running, the backup might never finish.)
It is possible to use 'cp' to make a backup, but not of a running database. You need to have an exclusive lock for the entire duration of the backup, so it's not really 'live'. You also need to be careful to copy all of sqlite's temp files as well as the main database.
I'd expect the sqlite3 ".backup" command to use the backup API.
If you cannot use the backup API, you must use another mechanism to prevent the database file from being modified while you're copying it.
Start a transaction with BEGIN IMMEDIATE:
After a BEGIN IMMEDIATE, no other database connection will be able to write to the database or do a BEGIN IMMEDIATE or BEGIN EXCLUSIVE. Other processes can continue to read from the database, however.
According to one of my posts (below) it seems that there is no such thing as a database in Oracle. What we call database in MySQL and MS-SQL is called schema in Oracle.
If that is the case, then why do the oracle docs mention the create database statement ?
For the record, I am using Oracle 11g and oracle SQL Developer GUI tool.
Post-
How to create a small and simple database using Oracle 11 g and SQL Developer?
The create database statement from oracle docs is given below. If there is no database concept, then how did this command come into the picture ?
CREATE DATABASE
CREATE DATABASE [ database ]
{ USER SYS IDENTIFIED BY password
| USER SYSTEM IDENTIFIED BY password
| CONTROLFILE REUSE
| MAXDATAFILES integer
| MAXINSTANCES integer
| CHARACTER SET charset
| NATIONAL CHARACTER SET charset
| SET DEFAULT
{ BIGFILE | SMALLFILE } TABLESPACE
| database_logging_clauses
| tablespace_clauses
| set_time_zone_clause
}... ;
There is concept of a "database" in Oracle. What the term "database" means in Oracle terms is different than what the term means in MySQL or SQL Server.
Since you are using the express edition, Oracle automatically runs the CREATE DATABASE statement as part of the installation process. You can only have 1 express edition database on a single machine. If you are installing a different edition, you can choose whether to have the installer create a database as part of the installation process or whether to do that manually via the CREATE DATABASE statement later. If you are just learning Oracle, you're much better off letting Oracle create the database for you at installation time-- you can only create the database via command-line tools (not SQL Developer) and it is rare that someone just starting out would need to tweak the database settings in a way that the installer didn't prmopt you for.
In Oracle, a "database" is a set of data files that includes the data files for the SYS and SYSTEM schemas which contain all the Oracle data dictionary tables, the data files for the TEMP tablespace where sorts and other temporary operations occur, and the data files for whatever schemas you want to create. In SQL Server and other RDBMSs, these would be separate "databases". In SQL Server, you have a master database, a tempdb database, additional database for different products (i.e. msdb for the SQL Server Agent), and then additional user-defined databases. In Oracle, these would all be separate schemas in a larger container that Oracle refers to as a "database".
Occasionally, a DBA will want to run multiple Oracle databases on the same server-- most commonly when there are different packaged applications that have different requirements about database versions or parameters. If you want to run application A that requires an 11.2 database and application B that doesn't support 11.2 yet, you would need to have two different databases on the server. The DBA could create a separate database and a separate instance but that doubles the memory requirements, doubles the number of background processes required to run the database, and generally makes things less scalable. It's necessary if you really want to run different versions of the database simultaneously but it's not ideal.
The person who answered your original question is correct. The DDL (Data Definition Language) above prepares a space for schemas, which is analogous to MySQL's 'database'. The above statement defines characteristics of the schemas, such as timezone, MBs of space for tables, encoding characterset, root account, etc. You would then issue DDL statements such as those in your other post to create schemas, which define what each user can see.
How to create a small and simple database using Oracle 11 g and SQL Developer ?
I am seeing too many errors and I cannot find any way to make a simple database.
For example
create database company;
Caused the following error:
Error starting at line 1 in command:
create database company
Error at Command Line:1 Column:0
Error report:
SQL Error: ORA-01501: CREATE DATABASE failed
ORA-01100: database already mounted
01501. 00000 - "CREATE DATABASE failed"
*Cause: An error occurred during create database
*Action: See accompanying errors.
EDIT-
This is completely different from MySQL and MS-SQL that I am familiar with.
Not as intuitive as I was expecting.
First off, what Oracle calls a "database" is generally different than what most other database products call a "database". A "database" in MySQL or SQL Server is much closer to what Oracle calls a "schema" which is the set of objects owned by a particular user. In Oracle, you would generally only have one database per server (a large server might have a handful of databases on it) where each database has many different schemas. If you are using the express edition of Oracle, you are only allowed to have 1 database per server. If you are connected to Oracle via SQL Developer, that indicates that you already have the Oracle database created.
Assuming that you really want to create a schema, not a database (using Oracle terminology), you would create the user
CREATE USER company
IDENTIFIED BY <<password>>
DEFAULT TABLESPACE <<tablespace to use for objects by default>>
TEMPORARY TABLESPACE <<temporary tablespace to use>>
You would then assign the user whatever privileges you wanted
GRANT CREATE SESSION TO company;
GRANT CREATE TABLE TO company;
GRANT CREATE VIEW TO company;
...
Once that is done, you can connect to the (existing) database as COMPANY and create objects in the COMPANY schema.
Actually the answer from Justin above could not be more incorrect. SQL Server and MySQL are for smallish databases. Oracle is for large enterprise databases, thus the difference in it's structure. And it is common to have more than one Oracle database on a server provided that the server is robust enough to handle the load. If you received the error posted above then you obviously are trying to create a new Oracle database and if you are doing that then you probably already understand the structure of an Oracle database. The likely scenario is that you attempted to create a database using dbca, it initially failed, but the binaries were created. You then adjusted your initial parameters and re-tried creating the database using dbca. However, the utility sees the binaries and folder structure for the database that you are creating so it thinks that the database already exists but is not mounted. Dropping the database and removing the binaries and folders as well as any other cleanup of the initial attempt should be done first, then try again.
From your question description, I think you were to create a database schema, not a database instance. In Oracle terminology, a database instance is a set of files in the file system. It's more like data files in MySQL. Whereas database in MySQL is somewhat equivalent to Oracle's schema.
To create a schema in Oracle: https://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_6014.htm
To create a database instance in Oracle (I personally prefer CDBA):
https://docs.oracle.com/cd/E11882_01/server.112/e25494/create.htm#ADMIN11068
Notice the Oracle Express edition does not support mounting more than one database instance at one time.