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Server Shadowing and Recovery
B.4 Shadow Site Failure and Journaling
B.4.1 Maximum Journal Size
The current maxima for the size of a journal are:
Number of blocks per disk: 524288
(This is
max_segments_per_disk * disk_blocks_per_segment
, or 16384 times
32.)
Number of disks per journal: 16.
B.5 Standby for Shadows
Shadowed sites can either be two nodes within a single cluster, or can be two
separate clusters. In the second case it is also possible to configure standby
servers on another node of each of these clusters, so that failure of a single node
within one of the shadow sites does not stop the shadow site from functioning.
Multiple concurrent copies of the server processes are allowed on each site.
This implies that up to four nodes can be configured to serve a particular key
range. (see Figure B–1).
Figure B–1 Four Node Shadow/Standby Configuration
Primary
Shadow
NODE A
Primary
Standby
NODE B
Cluster C1
Standby
Shadow
Secondary
Secondary
Cluster C2
NODE P
NODE Q
B.6 Performance
The performance of a shadow pair compares with a transaction which spans
two nodes, with the addition of one extra protocol message which is required to
ensure that the transactions are presented in the equivalent order.
B–4 Server Shadowing and Recovery