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WAL-mode File Format
(walformat.html)
1.3. The Wal-Index or "-shm" file
The wal-index file or "shm" file is not actually used as a file.
Rather, individual database clients mmap the shm file and use it
as shared memory for coordinating access to the database and as a cache
for quickly ...
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8+3 Filenames
(shortnames.html)
... Similarly, "app.db-wal" will become "app.wal" and
"app.db-shm" becomes "app.shm".
Note that it is very important that the database filename have some kind
of extension. If there is no extension, then SQLite creates auxiliary
filenames ...
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Write-Ahead Logging
(wal.html)
1. Overview
... The opening process must have write privileges for "-shm"
wal-index shared memory file associated with the database, if that
file exists, or else write access on the directory containing
the database file if the "-shm" file does not exist ...
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C API: Standard File Control Opcodes
(c3ref/c_fcntl_begin_atomic_write.html)
SQLITE_FCNTL_LOCKSTATE, SQLITE_FCNTL_GET_LOCKPROXYFILE, SQLITE_FCNTL_SET_LOCKPROXYFILE, SQLITE_FCNTL_LAST_ERRNO, SQLITE_FCNTL_SIZE_HINT, SQLITE_FCNTL_CHUNK_SIZE ...
... The SQLITE_FCNTL_CKPT_DONE opcode is invoked from within a checkpoint
in wal mode after the client has finished copying pages from the wal
file to the database file, but before the *-shm file is updated to
record the fact that the ...
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Temporary Files Used By SQLite
(tempfiles.html)
2.3. Shared-Memory Files
... The shared-memory file, if it exists, is located
in the same directory as the database file and has the same name as the
database file except with the 4 characters "-shm" appended.
Shared memory files only exist while running ...
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Result and Error Codes
(rescode.html)
6. Result Code Meanings
... SQLITE_IOERR indicating an I/O error
within the xShmMap method on the sqlite3_io_methods object
while trying to enlarge a "shm" file as part of
WAL mode transaction processing. This error may indicate that
the underlying filesystem volume is out of ...
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Compile-time Options
(compile.html)
9. Options To Omit Features
... SEH is used
to intercept errors that might occur while accessing the
memory-mapped shm file that are part of WAL mode processing. If
the operating system raised errors while SQLite is trying to access
the shm file, this option ...
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Database File Format
(fileformat.html)
4.6. WAL-Index Format
... The memory-mapped
file is in the same directory as the database and has the same name
as the database with a "-shm" suffix appended. Because
the wal-index is shared memory, SQLite does not support
journal_mode=WAL
on a ...
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