Transaction Processing
Distribution of data complicates tx processing ...
- potential for multiple copies of data to become inconsistent
- commit or abort must occur consistently on all nodes
Distributed tx processing handled by two-phase commit
- initiating site has transaction coordinator Ci ...
- waits for all other sites executing tx
T to "complete"
- sends
<prepare T> message to all other sites
- waits for
<ready T> response from all other sites
- if not received (timeout), or
<abort T> received, flag abort
- if all other sites respond
<ready T>, flag commit
- write
<commit T> or <abort T> to log
- send
<commit T> or <abort T> to all other sites
- non-initiating sites write log entries before responding
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