libSQL WAL API #1788
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libSQL WAL API #1788
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SQLite unconditionally checkpoints when the last connection is closed to a database. Let's add a libSQL extension API to give callers control over that.
This patch adds a libsql_wal_frame_count() API that the caller can use to determine how many frames there are in the WAL. You use the libsql_wal_frame_count() API together with the libsql_wal_get_frame() API, added in another patch, to read the raw WAL frames from a database and inject them into another WAL representing the copy of the database.
This adds a new xReadFrameRaw() function to the virtual WAL API, which upper layers can use to fetch the full frame, including the page number, that is useful for appending frames to a WAL.
This patch adds a libsql_wal_get_frame() API to read the raw WAL frame
from a database.
You can use the API as follows (omitting error handling) to obtain all
the WAL frames in a database:
```c
static int sync_db(sqlite3 *db_primary, sqlite3 *db_backup){
unsigned int max_frame;
libsql_wal_frame_count(db_primary, &max_frame);
for(int i=1; i<=max_frame; i++){
char frame[4096+24];
libsql_wal_get_frame(db_primary, i, frame, sizeof(frame));
}
}
```
```c
static void sync_db(sqlite3 *db_primary, sqlite3 *db_backup){
unsigned int max_frame;
libsql_wal_frame_count(db_primary, &max_frame);
libsql_wal_begin_commit(db_backup);
for(int i=1; i<=max_frame; i++){
char frame[4096+24];
libsql_wal_get_frame(db_primary, i, frame, sizeof(frame));
libsql_wal_insert_frame(db_backup, i, frame, sizeof(frame));
}
libsql_wal_end_commit(db_backup);
}
```
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This pull request adds a WAL API to libSQL, which allows callers to read frames from a database WAL and apply them.
The purpose of this API is to allow syncing the frames of one database WAL onto another. Omitting error handling, here's how you implement database syncing:
Fixes #200