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document the fact that LSN 0 is reserved

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Sears Russell 2011-03-25 20:24:40 +00:00
parent 5364377fd9
commit b20cd8cd0f
1 changed files with 10 additions and 0 deletions
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stasis/logger/logger2.h
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@ -115,6 +115,16 @@ struct stasis_log_t {
Append a log entry to the end of the log. Append a log entry to the end of the log.
This function assigns an LSN to the entry that is written. The choice of
LSN is up to the log implementation, with a few important restrictions.
First, LSN's must be strictly increasing (LSN stands for Log *sequence*
number, after all!). Next, LSN's must be greater than zero. LSN zero is
reserved for the version of the database before any log entries are
applied, so no valid log entry may have LSN = 0. At the time of this
writing, LSN -1 is INVALID_LSN. The other negative LSNs are reserved for
future use. @see constants.h for information about hard-coded constants.
@param log "this" log object @param log "this" log object
@param e The entry to be written to log. After the call returns, e->LSN will be the new entry's offset. @param e The entry to be written to log. After the call returns, e->LSN will be the new entry's offset.
@return 0 on success @return 0 on success