System tables and multiplex dbspace management [CR 375326]

Multiplex configuration information is found in the system table SYSIQFILE and in the following special system tables:

• IQ_MPX_INFO

• IQ_MPX_STATUS

• IQ_MPX_VERSIONLIST

For details, see Chapter 9, “System Tables,” in the Sybase IQ Reference Manual.

The following rules govern dbspace management in the multiplex:

• Each multiplex server has a set of rows in SYSIQFILE. This set includes:

  • One row for each shared main dbspace

  • One row for each temporary dbspace of the server

  • One row for the .message file (.iqmsg)

  • If it is a query server, one row for each local dbspace of the server

• The server_name column of SYSIQFILE identifies the server that owns the row. Each row that belongs to the write server has the empty string, ' ', as the server_name. Each row that belongs to a query server names that query server in the server_name column.

  Do not confuse owning a row in SYSIQFILE with owning the dbspace. For example, a shared main dbspace named main2 is owned by the write server, but each query server owns a row in SYSIQFILE for dbspace main2 with the query server’s server_name.

• Filenames may use either absolute or relative paths. On UNIX, they may also be UNIX links rather than actual files. The most flexible setup is to use relative paths for NFS files and, on UNIX, relative paths to links for raw devices.

• Filenames used for a shared main dbspace may differ across servers, either because the device names differ on different servers or because the DBA uses links with different names for each server.

• SYSFILE contains one row for each physical IQ dbspace file. Since there is one row in SYSIQFILE for each main dbspace for each server, there is a many-to-one relationship between the rows in SYSIQFILE and the rows in SYSFILE for shared main dbspace. All temporary and local dbspaces have exactly one row in SYSFILE and one row in SYSIQFILE.

• The query server rows in SYSIQFILE for a shared main dbspace are called aliases. The term alias may also refer to any row in SYSIQFILE that belongs to another server.