The information in this article applies to:
- Microsoft Access version 7.0
SUMMARY
Advanced: Requires expert coding, interoperability, and multiuser skills.
Replication of a database increases the size of the database. When you
replicate a database, Microsoft Access implements the following changes:
- It adds three new fields to each existing table in your database:
a unique identifier, a generation indicator, and a lineage indicator.
- It adds new system tables to your database: mSysSidetables, MsysErrors,
MSysSchemaProb, and MsysExchangeLog.
- It adds new properties to your database.
- It changes the behavior of AutoNumber fields.
- It increases the physical size of the database.
MORE INFORMATION
Besides being aware that replication makes the above changes, you should
also be aware that replication imposes the following two limitations on
your tables:
- First, the Microsoft Jet database engine allows a maximum of 2048 bytes
(not counting Memo or OLE Object fields) in a record. Replication uses
a minimum of 28 bytes to store unique identifiers and information about
changes to the record. If the record contains either Memo or OLE Object
fields, replication uses an additional 4 bytes for each of those fields.
You can calculate the total number of bytes available in a record in a
replicated table as follows:
2048 bytes - 28 bytes for replication overhead - (4 bytes * the
number of Memo fields) - (4 bytes * the number of OLE Object fields)
= the maximum number of bytes available
- Second, the Jet database engine allows a maximum of 255 fields in a
table of which at least three fields are used by replication. You can
calculate the total number of fields available in a replicated table
as follows:
255 fields - 3 system fields - the number of Memo and OLE Object
fields = the number of fields available
Most well-designed applications do not use all the available fields in a
table or all the available characters in a record. However, if you have a
large number of Memo fields or OLE Object fields in your table, you should
be aware of your remaining resources.
Just as the addition of three new fields to your tables adds to the size of
each record, the addition of new system tables adds to the size of your
database. Many of these new tables contain only a few records, but some of
the new tables can grow significantly depending upon the frequency of
synchronization between replicas.
The size of your database file can be significant for many reasons,
including the following:
- The Microsoft Jet data base engine supports files up to a maximum of 1
gigabyte in size.
- Many users have limited space available on their hard drives and the
creation of a replicable database that is larger than the original file
can use up all available disk space.
- If you choose to make a backup copy of the nonreplicable form of your
database, you must have sufficient space on your hard drive.
REFERENCES
For more information about replication in DAO, search for "replication,"
and then "replication fields" using the Microsoft Access for Windows 95
Help Index.