Reproduce SQLite WAL Checkpoint Starvation With One Forgotten Reader
The article, titled 'Reproduce SQLite WAL Checkpoint Starvation With One Forgotten Reader', explains a scenario where a single reader that fails to close its transaction can cause WAL checkpoint starvation in SQLite. The author describes how SQLite's Write-Ahead Log (WAL) mode relies on checkpoints to move data from the WAL file back into the main database file. However, if any reader holds a read transaction open, the checkpoint cannot advance past that reader's snapshot. This results in the WAL file growing indefinitely, potentially consuming excessive disk space and degrading performance. The article provides a step-by-step reproduction script and explains the underlying mechanism, including the role of the 'read mark' in the WAL header. The consequence is that developers must ensure all read transactions are properly closed to avoid unbounded WAL growth.
Unclosed read transactions in SQLite WAL mode can cause unbounded WAL file growth and performance degradation.