Icon Appendix C - System Capacities

The following is a detailed list of the capacities for the different components in DBISAM. Unless where noted all capacities are absolute and not dependent upon the underlying operating system or network.

CapacityDetails
# of BLOB Fields in a TableThe maximum number of BLOB fields in a table is 128.
# of Decimal Places in a BCD FieldThe maximum number of decimals places in a BCD field is 4.
# of Fields in TableThe maximum number of fields in a table is 1024.
# of Fields in an Index KeyThe maximum number of fields in an index key is 128.
# of Indexes in a TableThe maximum number of primary indexes in a table is 1. The maximum number of secondary indexes in a table is 30.
# of Open BLOBs in a TableThe maximum number of open BLOBs in a table is 128.
# of Open TablesThe maximum number of open tables is only limited by the available memory constraints of the operating system or hardware.

Information DBISAM has a limit of 4096 tables per database, but a single application can open the same table in the same database many times as well as open many tables from other databases.
# of Records in a TableThe maximum number of records in a table is 100 million under Linux, 200 million under Windows 95/98/ME, and up to 1 billion under Windows NT/2000/XP (see below).

Information The maximum number of records is affected by the current value of the TDBISAMEngine LargeFileSupport property. If LargeFileSupport is False (the default value), then the maximum number of records for Windows NT/2000/XP will be the same as with Windows 95/98/ME. If LargeFileSupport is True, then the maximum number of records increases to the figure above for Windows NT/2000/XP.
# of Records in a TransactionThe maximum number of records in a single transaction is only limited by the available memory constraints of the operating system or hardware.
# of Tables in a DatabaseThe maximum number of tables in a database is 4096 tables.
Size Of Database NamesThe maximum size of a database name is 60 bytes.
Size Of Field ConstraintThe maximum size of a field constraint expression is 100 bytes.
Size Of Field DescriptionsThe maximum size of a field description is 100 bytes.
Size Of Field NamesThe maximum size of a field name is 60 bytes.
Size Of Index NamesThe maximum size of an index name is 60 bytes.
Size Of Physical Table FilesThe maximum size of the physical files that make up a table - <TableName>.dat for data, <TableName>.idx for indexes, and <TableName>.blb for BLOBS, is 2,000,000,000 bytes under Linux, 4,000,000,000 bytes under Windows 95/98/ME, and up to 128,000,000,000 bytes under Windows NT/2000/XP (see below).

Information The maximum file size is affected by the current value of the TDBISAMEngine LargeFileSupport property. If LargeFileSupport is False (the default value), then the maximum file size for Windows NT/2000/XP will be the same as with Windows 95/98/ME. If LargeFileSupport is True, then the maximum file size increases to the figure above for Windows NT/2000/XP.
Size Of Table DescriptionsThe maximum size of a table description is 100 bytes.
Size Of Table NamesThe maximum size of a table name is 60 bytes.
Size of BLOB BlocksThe minimum BLOB block size is 64 bytes and the maximum BLOB block size is 64 kilobytes.
Size of BLOB FieldsThe maximum length of a BLOB field is 2 gigabytes.
Size of In-Memory TablesThe maximum length of an in-memory table is only limited by the available memory constraints of the operating system or hardware.
Size of Index KeysThe maximum size of an index key is 4096 bytes. The index key length is not an exact sum of the length of the fields present in the index key. The proper way to calculate the index key length is as follows:

For primary indexes the calculation is:

((Sum of field sizes) + Number of Fields in Index Key

For secondary indexes the calculation is:

((Sum of field sizes) + Number of Fields in Index Key + 4

The extra bytes for the number of fields are the NULL flags used to order the index keys properly based upon whether they are NULL or not.

The additional four bytes for secondary indexes is used to store a unique record ID which is essential for proper bookmark support.

Information The length of string fields in index keys includes the null terminator character. For example, if a string field has a length of 15 then its length in an index key would be 16.
Size of Index PagesThe minimum index page size is 1024 bytes and the maximum index page size is 16 kilobytes.
Size of RecordsThe maximum record size is 65280 bytes.
Size of String FieldsThe maximum length of a string field is 512 bytes. This figure does not include a NULL terminator character. The NULL terminator character is handled internally.
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