While installing SQLite I am getting message as
SQLite version 3.9.2 2015-11-02 18:31:45
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite>
what it means transient in-memory database?
The documentation says:
An SQLite database is normally stored in a single ordinary disk file. However, in certain circumstances, the database might be stored in memory.
[…]
When this is done, no disk file is opened. Instead, a new database is created purely in memory. The database ceases to exist as soon as the database connection is closed.
Related
The goal is to complete an online backup while other processes write to the database.
I connect to the sqlite database via the command line, and run
.backup mydatabase.db
During the backup, another process writes to the database and I immediately receive the message
Error: database is locked
and the backup disappears (reverts to a size of 0).
During the backup process there is a journal file, although it never gets very large. I checked that the journal_size_limit pragma is set to -1, which I believe means its unlimited. My understanding is that writes to the database should go to the journal during the backup process, but maybe I'm wrong. I'm new to sqlite and databases in general.
Am I going about this the wrong way?
If the sqlite3 backup writes "Error: database is locked", then you should use
sqlite3 source.db ".timeout 10000" ".backup backup.db"
See also Increase the lock timeout with sqlite, and what is the default values? about default timeouts (spoiler: it's zero) and now with backups solved you can switch SQLite to WAL mode (it supports multiple writers!).
//writing this as an answer so it would be easier to google this, thanks guys!
I have aborted vacuum with ctrl+c and deleted the journal (I thought it is useless for that case). Now it writes that the db is corrupt. I wonder if it is possible to mark the DB as non-corrupt without recreating it by translation to sql and back.
I am using sqlite3 Database for the database management for my AM1808 ARM9 based microprocessor.
I am using EMbedded Linux (V10.10 Lucid) and Gcc compiler for ARM.
My scenario is as following,
I have GSM moduled interfaced on UART. I am continuously synchronize my data with the server in background.
I am also accessing SQLIte database for other processes like read,write,view etc..
I have a single database connection.
I have simultaneous access to the Sqlite3.For the Multihandling sqlite3 with a single connection i have used Mutexs for the database lock. I have also used SQLITE3_BUSY flag for checking and all that.
Still i am missing my inserted record in the database, means database is not giving any error for the inserting record to the database.
So i can find that problem.I stuck here and i can not further proceed.
Please guide me. If you need than please tell me i will provide my code snippet.
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.
I am completely new to SQLite and I intend to use it in a M2M / client-server environment where a database is generated on the server, sent to the client as a file and used on the client for data lookup.
The question is: can I replace the whole database file while the client is using it at the same time?
The question may sound silly but the client is a Linux thin client and to replace the database file a temporary file would be renamed to the final file name. In Linux, a program which has still open the older version of the file will still access the older data since the old file is preserved by the OS until all file handles have been closed. Only new open()s will access the new version of the file.
So, in short:
client randomly accesses the SQLite database
a new version of the database is received from the server and written to a temporary file
the temporary file is renamed to the SQLite database file
I know it is a very specific question, but maybe someone can tell me if this would be a problem for SQLite or if there are similar methods to replace a database while the client is running. I do not want to send a bunch of SQL statements from the server to the client to update the database.
No, you cannot just replace an open SQLite3 DB file. SQLite will keep using the same file descriptor (or handle in Windows-speak), unless you close and re-open your database. More specifically:
Deleting and replacing an open file is either useless (Linux) or impossible (Windows). SQLite will never get to see the contents of the new file at all.
Overwriting an SQLite3 DB file is a recipe for data corruption. From the SQLite3 documentation:
Likewise, if a rogue process opens a
database file or journal and writes
malformed data into the middle of it,
then the database will become corrupt.
Arbitrarily overwriting the contents of the DB file can cause a whole pile of issues:
If you are very lucky it will just cause DB errors, forcing you to reopen the database anyway.
Depending on how you use the data, your application might just crash and burn.
Your application may try to apply an existing journal on the new file. Sounds painful? It is!
If you are really unlucky, the user will just get back invalid results from any queries.
The best way to deal with this would be a proper client-server implementation where the client DB file is updated from data coming from the server. In the long run that would allow for far more flexibility, while also reducing the bandwidth requirements by sending updates, rather than the whole file.
If that is not possible, you should update the client DB file in three discrete steps:
Send a message to the client application to close the DB. This allows the application to commit any changes, remove any journal files and clean-up its internal state.
Replace/Overwrite the file.
Send a message to the client application to re-open the DB. You would have to setup all prepared statements again, though.
If you do not want to close the DB file for some reason, then you should have your application - or even a separate process - update the original DB file using the new file as input. The SQLite3 backup API might be of interest to you in that case.