Resolving SQLITE_CORRUPT_VTAB in FTS5 Virtual Tables

Issue Overview: SQLITE_CORRUPT_VTAB Error in FTS5 Virtual Table Creation and Querying

The SQLITE_CORRUPT_VTAB error is a specific SQLite error code that indicates corruption or inconsistency in a virtual table. In the context of FTS5 (Full-Text Search version 5), this error typically arises when there is a mismatch between the virtual table’s structure and the underlying data it references. The error can occur during the creation of the virtual table, the insertion of data, or when querying the virtual table.

In the scenario described, the user attempted to create an FTS5 virtual table (fts_geoname) that references an existing table (geoname). The virtual table was designed to index specific columns (name, asciiname, alternatenames) from the geoname table. The user followed the standard procedure for creating the virtual table and inserting data into it. However, when attempting to query the virtual table using a full-text search, the SQLITE_CORRUPT_VTAB error was encountered.

The error suggests that the virtual table’s internal state is inconsistent with the data it is supposed to index. This inconsistency could be due to several factors, including incorrect column mappings, missing or mismatched row IDs, or issues with the underlying table’s structure. The error is particularly perplexing because the PRAGMA integrity_check command reported no errors, indicating that the database file itself is not corrupted.

Possible Causes: Misalignment Between Virtual Table and Content Table

The SQLITE_CORRUPT_VTAB error in this context is likely caused by a misalignment between the FTS5 virtual table and the content table it references. Specifically, the issue stems from the way the rowid is handled in the virtual table. In SQLite, the rowid is a unique identifier for each row in a table. When creating an FTS5 virtual table that references another table (the content table), it is crucial to ensure that the rowid of the virtual table correctly maps to the rowid (or a user-defined primary key) of the content table.

In the initial setup, the user created the FTS5 virtual table with the following command:

create virtual table fts_geoname using fts5(name, asciiname, alternatenames, content='geoname', content_rowid='geonameid');

Here, the content_rowid parameter is set to geonameid, which is the primary key of the geoname table. This means that the FTS5 virtual table expects the rowid of its entries to correspond to the geonameid values from the geoname table.

However, when inserting data into the FTS5 virtual table, the user executed the following command:

insert into fts_geoname (name, asciiname, alternatenames) select name, asciiname, alternatenames from geoname;

This command does not explicitly include the rowid (or geonameid) in the INSERT statement. As a result, the FTS5 virtual table does not receive the necessary rowid information, leading to an inconsistency between the virtual table and the content table. This inconsistency triggers the SQLITE_CORRUPT_VTAB error when querying the virtual table.

Troubleshooting Steps, Solutions & Fixes: Correcting the Rowid Mapping in FTS5 Virtual Tables

To resolve the SQLITE_CORRUPT_VTAB error, it is essential to ensure that the rowid of the FTS5 virtual table correctly maps to the rowid (or primary key) of the content table. This can be achieved by explicitly including the rowid in the INSERT statement when populating the virtual table.

The corrected INSERT statement should look like this:

insert into fts_geoname (rowid, name, asciiname, alternatenames) select geonameid, name, asciiname, alternatenames from geoname;

In this statement, the rowid column of the FTS5 virtual table is explicitly populated with the geonameid values from the geoname table. This ensures that the virtual table’s rowid correctly corresponds to the primary key of the content table, thereby maintaining the necessary alignment between the two tables.

After making this correction, the FTS5 virtual table should function as expected, and queries should no longer result in the SQLITE_CORRUPT_VTAB error. For example, the following query should now return the correct results:

select rowid, name from fts_geoname where fts_geoname match "Warsaw";

This query will search the fts_geoname virtual table for entries that match the term "Warsaw" and return the corresponding rowid and name values.

In addition to correcting the INSERT statement, it is also advisable to verify the integrity of the database and the virtual table after making changes. The PRAGMA integrity_check command can be used to ensure that the database file is not corrupted. If the integrity check passes, it is a good indication that the issue has been resolved.

Furthermore, it is important to ensure that the content table (geoname) is properly structured and that its primary key (geonameid) is correctly defined. The primary key should be unique and non-null for all rows in the table. If the primary key is not correctly defined, it could lead to inconsistencies when creating and querying the FTS5 virtual table.

In summary, the SQLITE_CORRUPT_VTAB error in this context is caused by a misalignment between the rowid of the FTS5 virtual table and the primary key of the content table. The error can be resolved by explicitly including the rowid in the INSERT statement when populating the virtual table. After making this correction, the virtual table should function correctly, and queries should no longer result in the SQLITE_CORRUPT_VTAB error. Additionally, it is important to verify the integrity of the database and ensure that the content table is properly structured to avoid similar issues in the future.