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Reclaiming Space
DuckDB uses a single-file format, which has some inherent limitations w.r.t. reclaiming disk space.
CHECKPOINT
To reclaim space after deleting rows, use the CHECKPOINT statement.
VACUUM
The VACUUM statement does not trigger vacuuming deletes and hence does not reclaim space.
Compacting a Database by Copying
To compact the database, you can create a fresh copy of the database using the COPY FROM DATABASE statement. In the following example, we first connect to the original database db1, then the new (empty) database db2. Then, we copy the content of db1 to db2.
ATTACH 'db1.db' AS db1;
ATTACH 'db2.db' AS db2;
COPY FROM DATABASE db1 TO db2;