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43 >PostgreSQL 7.4.1 Documentation</TH
67 >Chapter 25. Write-Ahead Logging (<ACRONYM
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99 >25.2. Future Benefits</A
102 > The UNDO operation is not implemented. This means that changes
103 made by aborted transactions will still occupy disk space and that
108 the status of transactions is still needed, since
109 transaction identifiers cannot be reused. Once UNDO is implemented,
113 > will no longer be required to be
114 permanent; it will be possible to remove
118 > at shutdown. (However, the urgency of
119 this concern has decreased greatly with the adoption of a segmented
120 storage method for <TT
124 necessary to keep old <TT
131 > With UNDO, it will also be possible to implement
138 > to allow partial rollback of
139 invalid transaction operations (parser errors caused by mistyping
140 commands, insertion of duplicate primary/unique keys and so on)
141 with the ability to continue or commit valid operations made by
142 the transaction before the error. At present, any error will
143 invalidate the whole transaction and require a transaction abort.
149 > offers the opportunity for a new method for
150 database on-line backup and restore (<ACRONYM
154 use this method, one would have to make periodic saves of data
155 files to another disk, a tape or another host and also archive the
159 > log files. The database file copy and the
160 archived log files could be used to restore just as if one were
161 restoring after a crash. Each time a new database file copy was
162 made the old log files could be removed. Implementing this
163 facility will require the logging of data file and index creation
164 and deletion; it will also require development of a method for
165 copying the data files (operating system copy commands are not
169 > A difficulty standing in the way of realizing these benefits is that
170 they require saving <ACRONYM
173 > entries for considerable
174 periods of time (e.g., as long as the longest possible transaction if
175 transaction UNDO is wanted). The present <ACRONYM
179 format is extremely bulky since it includes many disk page
180 snapshots. This is not a serious concern at present, since the
181 entries only need to be kept for one or two checkpoint intervals;
182 but to achieve these future benefits some sort of compressed
186 > format will be needed.
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233 >Write-Ahead Logging (<ACRONYM