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/**
* @defgroup LLADD_CORE Core API
*
* The minimal subset of Stasis necessary to implement transactional consistency.
*
* This module includes the standard API (excluding operations), the
* logger, the buffer mananger, and recovery code.
*
* In theory, the other .h files that are installed in /usr/include
* aren't needed for application developers.
*
* @todo Move as much of the stuff in lladd/ to src/lladd/ as possible. Alternatively, move all headers to lladd/, and be done with it!
*
*/
/**
@mainpage Introduction to Stasis
@section compiling Compiling and installation
Prerequisites:
- automake 1.8+: needed to build from CVS
- check: A unit testing
framework (needed to run the self-tests)
Optional:
- libconfuse: Used by older networking code to parse configuration options.
- BerkeleyDB: Used by the benchmarking code for purposes of comparison.
Development is currently performed under Debian's Testing branch.
To compile Stasis, first check out a copy with SVN. If you have commit access:
@verbatim
svn co --username username https://stasis.googlecode.com/svn/trunk stasis
@endverbatim
For anonymous checkout:
@verbatim
svn co http://stasis.googlecode.com/svn/trunk stasis
@endverbatim
then:
@code
$ ./reconf
$ ./configure --quiet
$ make -j4 > /dev/null
$ cd test/stasis
$ make check
@endcode
This will fail if your system defaults to an old (pre-1.7) version
of autotools. Fortunately, multiple versions of autotools may
exist on the same system. Execute the following commands to
compile with version 1.8 of autotools:
@code
$ ./reconf-1.8
$ ./configure --quiet
$ make -j4 > /dev/null
$ cd test/stasis
$ make check
@endcode
Of course, you can omit "--quiet" and "> /dev/null", but configure
and make both produce quite a bit of output that may obscure useful
warning messages.
'make install' installs the Stasis library and python SWIG
bindings, but none of the extra programs that come with Stasis.
utilities/ contains a number of utility programs that are useful
for debugging Stasis. The examples/ directory contains a number of
simple C examples.
@section usage Using Stasis in your software
Synopsis:
@include examples/ex1.c
Hopefully, Tbegin(), Talloc(), Tset(), Tcommit(), Tabort() and Tdealloc() are
self explanatory. If not, they are covered in detail elsewhere. Tinit() and
Tdeinit() initialize the library, and clean up when the program is finished.
Other partiularly useful functions are ThashCreate(), ThashDelete(),
ThashInsert(), ThashRemove(), and ThashLookup() which provide a
re-entrant linear hash implementation. ThashIterator() and
ThashNext() provide an iterator over the hashtable's values.
@subsection bootstrap Reopening a closed data store
Stasis imposes as little structure upon the application's data structures as
possible. Therefore, it does not maintain any information about the contents
or naming of objects within the page file. This means that the application
must maintain such information manually.
In order to facilitate this, Stasis provides the function TgetRecordType() and
guarantees that the first recordid returned by any allocation will point to
the same page and slot as the constant ROOT_RECORD. TgetRecordType
will return NULLRID if the record passed to it does not exist.
Therefore, the following code will safely initialize or reopen a data
store:
@include examples/ex2.c
@see test.c for a complete, executable example of reopeneing an existing store.
@todo Explain how to determine the correct value of rootEntry.size in the case
of a hashtable.
@see OPERATIONS for more operations that may be useful for your software.
@subsection consistency Using Stasis in multithreaded applications.
Unless otherwise noted, Stasis' operations are re-entrant. This
means that an application may call them concurrently without
corrupting Stasis' internal data structures. However, if two
threads attempt to write the same data value simultaneously, the
result is undefined.
In database terms, Stasis uses latches to protect its own data
structures' consistency (including those on disk), but does not
obtain short term read or write locks to protect data as it is
being written. This is less consistency than SQL's Level 0 (Dirty
Reads) provides. Some of Stasis' data structures do obtain short
read and write locks automatically. Refer to individual data
structues for more information.
Stasis' allocation functions, such as Talloc(), do not reuse space
that was freed by an ongoing transaction. This means that you may
safely overwrite freshly allocated space without writing undo
entries, and allows concurrent transactions to safely allocate
space.
From the point of view of conventional multithreaded software
development, Stasis closely matches the semantics provided by
typical operating system thread implementations. However, it
allows transactions to abort and rollback independently of each
other. This means that transactions may observe the effects of
transactions that will eventually abort.
Finally, Stasis asumes that each thread has its own transaction;
concurrent calls within the same transaction are not supported.
This restriction may be removed in the future.
@section selfTest The test suite
Stasis includes an extensive unit test suite which may be invoked
by running 'make check' in Stasis' root directory. Some of the
tests are for older, unmaintained code that was built on top of
Stasis. Running 'make check' in test/stasis runs all of the Stasis
tests without running the obsolete tests.
@section archictecture Stasis' structure
This section is geared toward people that would like to extend
Stasis. The OSDI paper provides a higher level description and
motivation for the architecture. This section describes naming
conventions used to distinguish between different portions of
Stasis, and provides an overview of memory management and mutex
acquisition conventions.
This section does not describe recovery, transaction initiation,
etc. Those methods change less frequently. Instead of focusing on
them, this text focuses on the issues faced by transactional data
structures.
Stasis components can be classified as follows:
- I/O utilities (file handles, OS compatibility wrappers)
- Write ahead logging component interfaces (logger.h, XXX)
- Write ahead logging component implementations (hash based buffer manager, in memory log, etc...)
- Page formats and associated operations (page/slotted.c page/fixed.c)
- Application visible methods (Talloc, Tset, ThashInsert, etc)
@subsection layoutNaming Directory layout
The Stasis repository contains the following "interesting" directories:
@par $STASIS/stasis/
Contains the header directory structure.
In theory, this contains all of the .h files that need to be
installed for a fully functional Stasis development environment.
In practice, .h files in src/ are also needed in some cases. The
separation of .h files between src/ and stasis/ continues for
various obscure reasons, including CVS's lack of a "move" command.
For now, .h files should be placed with similar .h files, or in
stasis/ if no such files exist.
The directory structure of stasis/ mirrors that of src/
@par $STASIS/src/
Contains the .c files
@par $STASIS/src/stasis
Contains Stasis and the implementations of its standard modules.
The subdirectories group files by the type of module they
implement.
@note By convention, when the rest of this document says
foo/, it is referring to two directories:
stasis/foo/ and src/stasis/foo/. Unless it's clear
from context, a file without an explicit directory name is in
stasis/ or src/stasis/. In order to refer to files
and directories outside of these two locations, but still in the
repository, this document will use the notation
$STASIS/dir.
@note This is done for brevity, and to avoid coupling documentation
to the (deprecated) placement of .h files under src/.
@note Example: The transactional data structure
implementations in operations/ can be found in
$STASIS/src/stasis/operations/ and
$STASIS/stasis/operations/.
@subsection Modules
Stasis is implemented in C, but is structured in a somewhat object
oriented style. There are a number of different "modules", for
lack of a better term. Each implementation in the module lives in
the module's subdirectory. Code that is common to many
implementation, and headers that define per-module functions live
in files named after the module.
Example: The io module contains the following files:
@code
io.h
io.c
io/handle.h
io/debug.c
io/file.c
io/memory.c
io/non_blocking.c
io/rangeTracker.h
io/rangeTracker.c
@endcode
In this case, rangeTracker.c and io.c are the only files containing
more than one non-static method, so they are the only ones that
have corresponding .h files. rangeTracker.c is implementing a data
structure that is being used by the other files. debug.c, file.c,
memory.c and non_blocking.c each implements a different type of
handle.
Some modules are simply groups of files that perform similar tasks,
or make use of the same set of interfaces (eg: page/ and
operations/). Files in these directories may make use of the same
utility functions, but aren't implementing the same interface.
Other modules provide multiple implementations of the same
interface (eg: io/ and logger/). C doesn't have
inheritance, so Stasis "fakes it" using one of two methods. In
both cases, a struct is defined to contain a void pointer, which
the implementation manually casts to the appropriate type:
@par Dispatch functions
The dispatch functions contain a switch statement or conditional
that decides which implementation to call. Calling convention:
@code bird_carry(african_swallow, coconut); @endcode
@par struct of function pointers
These functions use the following calling convention:
@code african_swallow->carry(african_swallow,coconut) @endcode
@subsection ioutil I/O utilities
The I/O utilities live in io/. They provide reentrant
interfaces. This was written to insulate Stasis from Linux's
ever-evolving I/O system calls, for portability, and to allow (for
example) in-memory operation.
@subsection walin WAL Modules
None of these modules understand page formats; at this level
everything is either
- a page with an LSN (a version number),or
- a log entry with an associated operation (redo / undo
functions).
Interesting files in this part of Stasis include logger2.c,
bufferManager.c, and recovery2.c.
@subsection page Page types
Page types define the layout of data on pages. Currently, all
pages contain a header with an LSN and a page type in it. This
information is used by recovery and the buffer manager to invoke
callbacks at appropriate times. (LSN-free pages are currently not
supported.)
XXX: This section is not complete.
@todo Discuss readRecord, writeRecord (high level page access
methods)
@todo Explain the latching convention. (Also, explain which
latches are not to be used by page implementations, and which
latches may not be used by higher level code.)
@par Registering new page type implementations
Page implementations are registered with Stasis by passing a
page_impl struct into registerPageType(). page_impl.page_type
should contain an integer that is unique across all page types,
while the rest of the fields contain function pointers to the page
type's implementation.
@par Pointer arithmetic
Stasis page type implementations typically do little more than
pointer arithmetic. However, implementing page types cleanly and
portably is a bit tricky. Stasis has settled upon a compromise in
this matter. Its page file formats are compatible within a single
architecture, but not across systems with varying lengths of
primitive types, or that vary in endianess.
Over time, types that vary in length such as "int", "long", etc
will be removed from Stasis, but their usage still exists in a few
places. Once they have been removed, file compatibility problems
should be limited to endianness (though application code will still
be free to serialize objects in a non-portable manner).
Most page implementations leverage C's pointer manipulation
semantics to lay out pages. Rather than casting pointers to
char*'s and then manually calculating byte offsets using sizeof(),
the existing page types prefer to cast pointers to appropriate
types, and then add or subtract the appropriate number of values.
For example, instead of doing this:
@code
// p points to an int, followed by a two bars, then the foo whose address
// we want to calculate
int * p;
foo* f = (foo*)( ((char*)p) + sizeof(int) + 2 * sizeof(bar))
@endcode
the implementations would do this:
@code
int * p;
foo * f = (foo*)( ((bar*)(p+1)) + 2 )
@endcode
The main disadvantage of this approach is the large number of ()'s
involved. However, it lets the compiler deal with the underlying
multiplications, and often reduces the number of casts, leading to
slightly more readable code. Take this implementation of
page_type_ptr(), for example:
@code
int * page_type_ptr(Page *p) { return ( (int*)lsn_ptr(Page *p) ) - 1; }
@endcode
Here, the page type is stored as an integer immediately before the
lsn_ptr. Using arithmetic over char*'s would require an extra
cast to char*, and a multiplication by sizeof(int).
@par A note on storage allocation
Finally, while Stasis will correctly call appropriate functions
when it encounters a properly registered third party page type, it
currently provides few mechanisms to allocate such pages in the
first place. There are examples of three approaches in the current
code base:
# Implement a full-featured, general purpose allocator, like the
one in alloc.h. This is more difficult than it sounds.
# Allocate entire regions at a time, and manually initialize pages
within them. arrayList.h attempts to do this, but gets it wrong
by relying upon lazy initialization to eventually set page types
correctly. Doing so is problematic if the page was deallocated,
then reused without being reset.
# Allocate a single page at a time using TallocPage(), and
TsetPage(). This is currently the msot attractive route, though
TsetPage() does not call pageLoaded() when it resets page types,
which can lead to trouble.
@see page.h, fixed.h, and slotted.h for more information on the
page API's, and the implementations of two common page formats.
@subsection appfunc Application visible methods
These methods start with "T". Look at the examples above. These
are the "wrapper functions" from the OSDI paper. They are
supported by operation implementations, which can be found in the
operations/ directory.
@section extending Implementing you own operations
@todo Provide a tutorial that explains how to extend Stasis with new operations.
@see increment.h for an example of a very simple logical operation.
@see linearHashNTA.h for a more sophisticated example that makes use of Nested Top Actions.
*/
/**
* @defgroup OPERATIONS Logical Operations
*
* Implementations of logical operations, and the interfaces that allow new operations to be added.
*
* @todo Write a brief howto to explain the implementation of new operations.
*
*/
/**
* @file
*
* Defines Stasis' primary interface.
*
*
*
* @todo error handling
*
* @ingroup LLADD_CORE
* $Id$
*/
#ifndef __TRANSACTIONAL_H__
#define __TRANSACTIONAL_H__
#include "common.h"
BEGIN_C_DECLS
/**
* represents how to look up a record on a page
* @todo recordid.page should be 64bit.
* @todo int64_t (for recordid.size) is a stopgap fix.
*/
typedef struct {
int page; // XXX needs to be pageid_t, but that breaks unit tests.
int slot;
int64_t size; //signed long long size;
} recordid;
typedef struct {
size_t offset;
size_t size;
// unsigned fd : 1;
} blob_record_t;
extern const recordid ROOT_RECORD;
extern const recordid NULLRID;
/**
If a recordid's slot field is set to this, then the recordid
represents an array of fixed-length records starting at slot zero
of the recordid's page.
@todo Support read-only arrays of variable length records, and then
someday read / write / insert / delete arrays...
*/
#define RECORD_ARRAY (-1)
#include "operations.h"
/**
* Currently, Stasis has a fixed number of transactions that may be
* active at one time.
*/
#define EXCEED_MAX_TRANSACTIONS 1
/**
* @param xid transaction ID
* @param LSN last log that this transaction used
*/
typedef struct {
int xid;
long LSN;
} Transaction;
/**
* Initialize Stasis. This opens the pagefile and log, initializes
* subcomponents, and runs recovery.
*
* @return 0 on success
*/
int Tinit();
/**
* Start a new transaction, and return a new transaction id (xid).
*
* @return positive transaction ID (xid) on success, negative return value on error
*/
int Tbegin();
/**
* Used when extending Stasis.
* Operation implementors should wrap around this function to provide more mnuemonic names.
*
* @param xid The current transaction.
* @param rid The record the operation pertains to. For some logical operations, this will be a dummy record.
* @param dat Application specific data to be recorded in the log (for undo/redo), and to be passed to the implementation of op.
* @param op The operation's offset in operationsTable
*
* @see operations.h set.h
*/
compensated_function void Tupdate(int xid, recordid rid,
const void *dat, int op);
compensated_function void TupdateStr(int xid, recordid rid,
const char *dat, int op);
compensated_function void TupdateRaw(int xid, recordid rid,
const void *dat, int op);
compensated_function void TupdateDeferred(int xid, recordid rid,
const void *dat, int op);
/**
* @param xid transaction ID
* @param rid reference to page/slot
* @param dat buffer into which data goes
*/
compensated_function void Tread(int xid, recordid rid, void *dat);
compensated_function void TreadStr(int xid, recordid rid, char *dat);
/**
* Commit an active transaction. Each transaction should be completed
* with exactly one call to Tcommit() or Tabort().
*
* @param xid transaction ID
* @return 0 on success
*/
int Tcommit(int xid);
/**
* Abort (rollback) an active transaction. Each transaction should be
* completed with exactly one call to Tcommit() or Tabort().
*
* @param xid transaction ID
* @return 0 on success, -1 on error.
*/
int Tabort(int xid);
/**
* Cleanly shutdown Stasis. After this function is called, you should
* call Tinit() before attempting to access data stored in Stasis.
* This function flushes all pages, cleans up log, and frees any
* resources that Stasis is holding.
*
* @return 0 on success
*/
int Tdeinit();
/**
* Uncleanly shutdown Stasis. This function frees any resources that
* Stasis is holding, and flushes the log, but it does not flush dirty
* pages to disk. This is used by testing to exercise the recovery
* logic.
*
* @return 0 on success
*/
int TuncleanShutdown();
/**
* Used by the recovery process.
* Revives Tprepare'ed transactions.
*
* @param xid The xid that is to be revived.
* @param lsn The lsn of that xid's most recent PREPARE entry in the log.
*/
void Trevive(int xid, long lsn);
/**
* Used by the recovery process.
*
* Sets the number of active transactions.
* Should not be used elsewhere.
*
* @param xid The new active transaction count.
*/
void TsetXIDCount(int xid);
/**
* Checks to see if a transaction is still active.
*
* @param xid The transaction id to be tested.
* @return true if the transacation is still running, false otherwise.
*/
int TisActiveTransaction(int xid);
/**
This is used by log truncation.
*/
lsn_t transactions_minRecLSN();
/**
Report Stasis' current durablity guarantees.
@return VOLATILE if the data will be lost after Tdeinit(), or a
crash, PERSISTENT if the data will be written back to disk after
Tdeinit(), but may be corrupted at crash, or DURABLE if Stasis will
apply committed transactions, and roll back active transactions
after a crash.
*/
int TdurabilityLevel();
END_C_DECLS
#endif