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Eric Brewer 2004-10-23 02:34:43 +00:00
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doc/paper/LLADD-Freenix.tex
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@ -509,8 +509,7 @@ make it easy to implement custom data structures for use within safe,
multi-threaded transactions. Clearly, an additional mechanism is needed. multi-threaded transactions. Clearly, an additional mechanism is needed.
The solution is to allow portions of an operation to ``commit'' before The solution is to allow portions of an operation to ``commit'' before
the operation returns. the operation returns.\footnote{We considered the use of nested top actions, which LLADD could easily
\footnote{We considered the use of nested top actions, which LLADD could easily
support. However, we currently use the slightly simpler (and lighter-weight) support. However, we currently use the slightly simpler (and lighter-weight)
mechanism described here. If the need arises, we will add support mechanism described here. If the need arises, we will add support
for nested top actions.} for nested top actions.}
@ -565,7 +564,7 @@ such a tool could easily be applied to existing LLADD operations.
Note that the ARIES algorithm is extremely complex, and we have left Note that the ARIES algorithm is extremely complex, and we have left
out most of the details needed to understand how ARIES works, or to out most of the details needed to understand how ARIES works, or to
implement it correctly.\footnote{The original ARIES paper is around 70 pages, and the ARIES/IM paper~\cite{ariesim}, which coversd index implementation is roughly the same length.} Yet, we believe we have covered everything that a programmer needs implement it correctly.\footnote{The original ARIES paper is around 70 pages, and the ARIES/IM paper~\cite{ariesim}, which covers index implementation is roughly the same length.} Yet, we believe we have covered everything that a programmer needs
to know in order to implement new data structures using the to know in order to implement new data structures using the
functionality that ARIES provides. This was possible due to the encapsulation functionality that ARIES provides. This was possible due to the encapsulation
of the ARIES algorithm inside of LLADD, which is the feature that of the ARIES algorithm inside of LLADD, which is the feature that
@ -600,7 +599,7 @@ Currently LLADD imposes two requirements on page layouts. The first
32 bits must contain an LSN for recovery purposes, 32 bits must contain an LSN for recovery purposes,
and the second 32 bits must contain the page type (since we allow multple page formats). and the second 32 bits must contain the page type (since we allow multple page formats).
Although it ships with basic operations that support variable length Although it ships with basic operations that support variable-length
records, hash tables and other common data types, our goal is to records, hash tables and other common data types, our goal is to
decouple all decisions regarding data format from the implementation decouple all decisions regarding data format from the implementation
of the logging and recovery systems. Therefore, the preceeding section of the logging and recovery systems. Therefore, the preceeding section
@ -609,16 +608,16 @@ the purpose of the performance numbers in our evaluation section are
not to validate our hash table, but to show that the underlying architecture not to validate our hash table, but to show that the underlying architecture
is able to efficiently support interesting data structures. is able to efficiently support interesting data structures.
Despite the complexity of the interactions between its modules, the Despite the complexity of the interactions among its modules, the
basic ARIES algorithm itself is quite simple. Therefore, in order to basic ARIES algorithm itself is quite simple. Therefore, in order to
keep LLADD simple, we started with a set of modules, and iteratively keep LLADD simple, we started with a set of modules, and iteratively
refined the boundaries between these modules. Figure~\ref{cap:LLADD-Architecture} presents the resulting architecture. The refined the boundaries among these modules. Figure~\ref{cap:LLADD-Architecture} presents the resulting architecture. The
core of the LLADD library is quite small at 2218 lines of code, 2155 core of the LLADD library is quite small at 2218 lines of code, 2155
lines of implementations of operations and other extensions, and 408 lines of implementations of operations and other extensions, and 408
lines of installable header files.\footnote{These counts were generated using David lines of installable header files.\footnote{These counts were generated using David
A. Wheeler's {\tt SLOCCount}. \cite{sloccount}} The code has been documented extensively, A. Wheeler's {\tt SLOCCount}. \cite{sloccount}} The code has been documented extensively,
and we hope that we have exposed most of the subtle interactions and we hope that we have exposed most of the subtle interactions
between internal modules in the online documentation. among internal modules in the online documentation.
As LLADD has evolved, many of its sub-systems have been incrementally As LLADD has evolved, many of its sub-systems have been incrementally
improved, and we believe that the current set of modules is amenable improved, and we believe that the current set of modules is amenable
@ -655,7 +654,7 @@ into subsystems with simple interfaces is obvious. We are able to
use standard unit-testing techniques to test each of LLADD's subsystems use standard unit-testing techniques to test each of LLADD's subsystems
independently, and have documented both external and internal interfaces, independently, and have documented both external and internal interfaces,
making it easy to add new tests and debug old ones. Furthermore, by making it easy to add new tests and debug old ones. Furthermore, by
adding a 'simulate crash' operation to a few of the key components, adding a ``simulate crash'' operation to a few of the key components,
we can simulate application level crashes by clearing LLADD's internal we can simulate application level crashes by clearing LLADD's internal
state, re-initializing the library and verifying that recovery was state, re-initializing the library and verifying that recovery was
successful. These tests currently cover approximately successful. These tests currently cover approximately
@ -679,10 +678,10 @@ A more interesting set of performance requirements are imposed by
multithreaded workloads. Each module of LLADD is reentrant, and a multithreaded workloads. Each module of LLADD is reentrant, and a
C preprocessor directive allows the entire library to be instrumented C preprocessor directive allows the entire library to be instrumented
in order to profile latching behavior, which is useful both for perfomance in order to profile latching behavior, which is useful both for perfomance
tuning and for debugging purposes. A thread that is not involved in tuning and for debugging. A thread that is not involved in
an I/O request never needs to wait for a latch held by a thread that an I/O request never needs to wait for a latch held by a thread that
is waiting for I/O.% is waiting for I/O.%
\footnote{Strictly speaking, this statement is only true for the LLADD's core. \footnote{Strictly speaking, this statement is only true for LLADD's core.
However, there are variants of most popular data structures that allow However, there are variants of most popular data structures that allow
us to preserve these invariants. LLADD can correctly support operations us to preserve these invariants. LLADD can correctly support operations
whether or not they have these properties.% whether or not they have these properties.%