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  1934   1934          DELETE statement executed by the user. This means that any operation
  1935   1935          on an FTS3/4 table may turn out to be surprisingly slow, as FTS3/4 
  1936   1936          may unpredictably choose to merge together two or more large b-trees
  1937   1937          within it. FTS5 uses incremental merging by default, which limits
  1938   1938          the amount of processing that may take place within any given 
  1939   1939          INSERT, UPDATE or DELETE operation.
  1940   1940   </ul>
         1941  +
         1942  +<h1 id=appendix_b nonumber tags="fts5 shadow tables">
         1943  +  Appendix B: Shadow tables created by FTS5
         1944  +</h1>
         1945  +
         1946  +<p>
         1947  +When an FTS5 virtual table is created in a database, between 3 and 5 real
         1948  +tables are created in the database. These are known as "shadow" tables, and are
         1949  +used by the virtual table module to store persistent data. They should not
         1950  +be accessed directly by the user. Many other virtual table modules, including
         1951  +[FTS3] and [rtree], also create and use shadow tables.
         1952  +
         1953  +<p>FTS5 creates the following shadow tables. In each case the actual table name
         1954  +is based on the name of the FTS5 virtual table (in the following table, replace
         1955  +&lt;name&gt; with the name of the virtual table to find the actual shadow
         1956  +table name).
         1957  +
         1958  +<table striped=1>
         1959  +<tr><th>Table&nbsp;Name<th>Contents
         1960  +<tr><td>&lt;name&gt;_data<td> This table contains most of the full-text index data.
         1961  +<tr><td>&lt;name&gt;_idx<td> This table contains the remainder of the full-text
         1962  +index data. It is almost always much smaller than the &lt;name&gt;_data table.
         1963  +<tr><td>&lt;name&gt;_config<td> Contains the values of persistent
         1964  +configuration parameters.
         1965  +<tr><td>&lt;name&gt;_content<td> Contains the actual data inserted into the 
         1966  +FTS5 table. This shadow table is not present for 
         1967  +[FTS5 contentless tables | contentless] or 
         1968  +[FTS5 external content tables|external content] FTS5 tables.
         1969  +<tr><td>&lt;name&gt;_docsize<td> Contains the size of each column of each
         1970  +row in the virtual table in tokens. This shadow table is not present if 
         1971  +the [FTS5 columnsize option|"columnsize" option] is set to 0.
         1972  +</table>
         1973  +
         1974  +
         1975  +
         1976  +