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@@ -1,10 +1,15 @@
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-head 1.9;
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+head 1.10;
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access;
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symbols;
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locks; strict;
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comment @# @;
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+1.10
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+date 2010.09.14.00.33.57; author rusty; state Exp;
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+branches;
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+next 1.9;
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+
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1.9
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date 2010.09.09.07.25.12; author rusty; state Exp;
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branches;
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@@ -56,9 +61,9 @@ desc
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@
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-1.9
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+1.10
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log
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-@Extension mechanism.
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+@Tracing attribute, talloc support.
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@
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text
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@#LyX 1.6.5 created this file. For more info see http://www.lyx.org/
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@@ -116,8 +121,8 @@ Rusty Russell, IBM Corporation
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\change_deleted 0 1283307542
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26-July
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-\change_inserted 0 1284016854
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-9-September
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+\change_inserted 0 1284423485
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+14-September
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\change_unchanged
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-2010
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\end_layout
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@@ -539,6 +544,17 @@ The tdb_open() call was expanded to tdb_open_ex(), which added an optional
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\begin_layout Subsubsection
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Proposed Solution
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+\change_inserted 0 1284422789
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+
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+\begin_inset CommandInset label
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+LatexCommand label
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+name "attributes"
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+
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+\end_inset
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+
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+
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+\change_unchanged
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+
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\end_layout
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\begin_layout Standard
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@@ -1352,13 +1368,69 @@ Proposed Solution
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\begin_layout Standard
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-\change_inserted 0 1284016847
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+\change_inserted 0 1284422552
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We often have extra padding at the tail of a record.
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If we ensure that the first byte (if any) of this padding is zero, we will
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have a way for future changes to detect code which doesn't understand a
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new format: the new code would write (say) a 1 at the tail, and thus if
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there is no tail or the first byte is 0, we would know the extension is
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not present on that record.
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+\end_layout
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+
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+\begin_layout Subsection
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+
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+\change_inserted 0 1284422568
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+TDB Does Not Use Talloc
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+\end_layout
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+
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+\begin_layout Standard
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+
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+\change_inserted 0 1284422646
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+Many users of TDB (particularly Samba) use the talloc allocator, and thus
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+ have to wrap TDB in a talloc context to use it conveniently.
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+\end_layout
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+
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+\begin_layout Subsubsection
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+
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+\change_inserted 0 1284422656
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+Proposed Solution
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+\end_layout
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+
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+\begin_layout Standard
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+
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+\change_inserted 0 1284423065
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+The allocation within TDB is not complicated enough to justify the use of
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+ talloc, and I am reluctant to force another (excellent) library on TDB
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+ users.
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+ Nonetheless a compromise is possible.
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+ An attribute (see
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+\begin_inset CommandInset ref
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+LatexCommand ref
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+reference "attributes"
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+
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+\end_inset
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+
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+) can be added later to tdb_open() to provide an alternate allocation mechanism,
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+ specifically for talloc but usable by any other allocator (which would
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+ ignore the
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+\begin_inset Quotes eld
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+\end_inset
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+
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+context
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+\begin_inset Quotes erd
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+\end_inset
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+
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+ argument).
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+\end_layout
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+
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+\begin_layout Standard
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+
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+\change_inserted 0 1284423042
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+This would form a talloc heirarchy as expected, but the caller would still
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+ have to attach a destructor to the tdb context returned from tdb_open to
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+ close it.
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+ All TDB_DATA fields would be children of the tdb_context, and the caller
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+ would still have to manage them (using talloc_free() or talloc_steal()).
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\change_unchanged
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\end_layout
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@@ -1938,7 +2010,7 @@ status open
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\begin_layout Plain Layout
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-\change_inserted 0 1283310945
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+\change_inserted 0 1284424151
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Using
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\begin_inset Formula $2^{16+N*3}$
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\end_inset
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@@ -1949,6 +2021,8 @@ means 0 gives a minimal 65536-byte zone, 15 gives the maximal
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byte zone.
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Zones range in factor of 8 steps.
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+ Given the zone size for the zone the current record is in, we can determine
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+ the start of the zone.
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\change_unchanged
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\end_layout
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@@ -2393,6 +2467,8 @@ TDB Does Not Have Snapshot Support
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\begin_layout Subsubsection
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Proposed Solution
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+\change_deleted 0 1284423472
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+
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\end_layout
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\begin_layout Standard
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@@ -2405,7 +2481,23 @@ use a real database
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\begin_inset Quotes erd
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\end_inset
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+
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+\change_inserted 0 1284423891
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+
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+\change_deleted 0 1284423891
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.
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+
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+\change_inserted 0 1284423901
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+ (but see
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+\begin_inset CommandInset ref
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+LatexCommand ref
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+reference "replay-attribute"
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+
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+\end_inset
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+
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+).
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+\change_unchanged
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+
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\end_layout
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\begin_layout Standard
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@@ -2428,6 +2520,8 @@ This would not allow arbitrary changes to the database, such as tdb_repack
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\begin_layout Standard
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We could then implement snapshots using a similar method, using multiple
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different hash tables/free tables.
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+\change_inserted 0 1284423495
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+
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\end_layout
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\begin_layout Subsection
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@@ -2447,6 +2541,18 @@ Proposed Solution
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\end_layout
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\begin_layout Standard
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+
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+\change_inserted 0 1284424201
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+None (but see
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+\begin_inset CommandInset ref
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+LatexCommand ref
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+reference "replay-attribute"
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+
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+\end_inset
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+
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+).
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+
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+\change_unchanged
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We could solve a small part of the problem by providing read-only transactions.
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These would allow one write transaction to begin, but it could not commit
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until all r/o transactions are done.
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@@ -2632,6 +2738,53 @@ At some later point, a sync would allow recovery of the old data into the
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free lists (perhaps when the array of top-level pointers filled).
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On crash, tdb_open() would examine the array of top levels, and apply the
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transactions until it encountered an invalid checksum.
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+\change_inserted 0 1284423555
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+
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+\end_layout
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+
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+\begin_layout Subsection
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+
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+\change_inserted 0 1284423617
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+Tracing Is Fragile, Replay Is External
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+\end_layout
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+
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+\begin_layout Standard
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+
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+\change_inserted 0 1284423719
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+The current TDB has compile-time-enabled tracing code, but it often breaks
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+ as it is not enabled by default.
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+ In a similar way, the ctdb code has an external wrapper which does replay
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+ tracing so it can coordinate cluster-wide transactions.
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+\end_layout
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+
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+\begin_layout Subsubsection
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+
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+\change_inserted 0 1284423864
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+Proposed Solution
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+\begin_inset CommandInset label
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+LatexCommand label
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+name "replay-attribute"
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+
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+\end_inset
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+
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+
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+\end_layout
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+
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+\begin_layout Standard
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+
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+\change_inserted 0 1284423850
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+Tridge points out that an attribute can be later added to tdb_open (see
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+
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+\begin_inset CommandInset ref
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+LatexCommand ref
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+reference "attributes"
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+
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+\end_inset
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+
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+) to provide replay/trace hooks, which could become the basis for this and
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+ future parallel transactions and snapshot support.
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+\change_unchanged
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+
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\end_layout
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\end_body
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@@ -2639,6 +2792,33 @@ At some later point, a sync would allow recovery of the old data into the
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@
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+1.9
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+log
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+@Extension mechanism.
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+@
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+text
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+@d56 2
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+a57 2
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+\change_inserted 0 1284016854
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+9-September
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+d479 11
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+d1303 1
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+a1303 1
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+\change_inserted 0 1284016847
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+d1310 56
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+d1945 1
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+a1945 1
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+\change_inserted 0 1283310945
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+d1956 2
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+d2402 2
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+d2416 4
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+d2421 12
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+d2455 2
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+d2476 12
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+d2673 47
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+@
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+
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+
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1.8
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log
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@Remove bogus footnote
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Rusty Russell