{ dbeng12 | dbsrv12  }  -wc[ + | - ] ...

All operating systems and servers.

The difference between the write checksums (enabled with the -wc option) and global checksums (creating a database with checksums enabled) is that with -wc database pages are checksummed only when they are written out to disk. Pages that are read from disk are only verified if a checksum value was calculated before the pages were written. If a database has checksums enabled, checksums are calculated for all pages when they are written and checksums are verified for all pages when they are read.

If the database server detects that the database is running on Windows Mobile or a removable storage device, such as a network share or USB device, then the database server automatically enables global checksums for all database pages.

By default, databases created with version 10 and 11 of SQL Anywhere do not have global checksums enabled. If you start a database created with SQL Anywhere 11 on a version 12 database server, then by default the database server creates write checksums for pages when they are written to disk (-wc+). Version 12 databases have global checksums enabled by default, so the database server defaults to -wc- for these databases because by default all database pages have checksums. You can use either the -wc option or the START DATABASE statement to change the database server's checksum behavior if you do not want to use the default checksum settings.

You can check whether a database was created with global checksums enabled by executing the following statement:

SELECT DB_PROPERTY ( 'Checksum' );

You can check whether write checksums are enabled for write I/O operations only by executing the following statement:

SELECT DB_PROPERTY ( 'WriteChecksum' );

• Using checksums to detect corruption
• -wc dbeng12/dbsrv12 server option
• START DATABASE statement