On Tue, Feb 26, at Secondly and the reason I wanted to enter the IRC on this occasionI am trying to follow the instruction:
If shared-cache mode is enabled and a thread establishes multiple connections to the same database, the connections share a single data and schema cache. This can significantly reduce the quantity of memory and IO required by the system.
Prior to this change, there were restrictions on passing database connections between threads. Those restrictions were dropped in 3.
This document describes shared-cache mode as of version 3.
Shared-cache mode changes the semantics of the locking model in some cases. The details are described by this document. Shared-Cache Locking Model Externally, from the point of view of another process or thread, two or more database connections using a shared-cache appear as a single connection.
The locking protocol used to arbitrate between multiple shared-caches or regular database users is described elsewhere. Figure 1 Figure 1 depicts an example runtime configuration where three database connections have been established.
Connection 1 is a normal SQLite database connection. Connections 2 and 3 share a cache The normal locking protocol is used to serialize database access between connection 1 and the shared cache.
The internal protocol used to serialize or not, see "Read-Uncommitted Isolation Mode" below access to the shared-cache by connections 2 and 3 is described in the remainder of this section. There are three levels to the shared-cache locking model, transaction level locking, table level locking and schema level locking.
They are described in the following three sub-sections. Transaction Level Locking SQLite connections can open two kinds of transactions, read and write transactions. This is not done explicitly, a transaction is implicitly a read-transaction until it first writes to a database table, at which point it becomes a write-transaction.
At most one connection to a single shared cache may open a write transaction at any one time. This may co-exist with any number of read transactions. Table Level Locking When two or more connections use a shared-cache, locks are used to serialize concurrent access attempts on a per-table basis.
Tables support two types of locks, "read-locks" and "write-locks".
Locks are granted to connections - at any one time, each database connection has either a read-lock, write-lock or no lock on each database table. At any one time, a single table may have any number of active read-locks or a single active write lock.
To read data a table, a connection must first obtain a read-lock. To write to a table, a connection must obtain a write-lock on that table.
Once a connection obtains a table lock, it is not released until the current transaction read or write is concluded. A database connection in read-uncommitted mode does not attempt to obtain read-locks before reading from database tables as described above.
This can lead to inconsistent query results if another database connection modifies a table while it is being read, but it also means that a read-transaction opened by a connection in read-uncommitted mode can neither block nor be blocked by any other connection.
Read-uncommitted mode has no effect on the locks required to write to database tables i. The following special rules also apply: Before executing a statement that modifies the database schema i. And a connection could only share cache with another connection in the same thread.
These restrictions were dropped beginning with SQLite version 3. This restriction was removed in SQLite version 3. Enabling Shared-Cache Mode Shared-cache mode is enabled on a per-process basis.
Using the C interface, the following API can be used to globally enable or disable shared-cache mode:Django login error: “attempt to write a readonly database” in IIS Hot Network Questions 2-Torsion in Jacobians of Curves Over Finite Fields.
Despite the database file being writable to the user as it should be. In PHP, this looks something like: SQLSTATE[HY]: General error: 14 unable to open database file.
The only way to access the database is via methods on the Transaction object. And creating a Transaction means acquiring a lock. And creating a Transaction means acquiring a lock. Together, these two restrictions make it impossible for two different threads to access the database at the same time.
Looks like the user that is running the web server doesn't have write access to the database file. Have a question about this project?
Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Question 2: I can move the file in the file system while the connection is open (deletion is not possible). The database then becomes readonly, for whatever reason. If I move it back, it works as if nothing happened.
attempt to write a readonly database 3Django 学习流程精简.