In order to allow linking of hamsterdb with more open source projects, i added FOSS license exceptions. These exceptions allow linking with BSD licensed libraries, Apache, LGPL and others.
Here’s the legal stuff and the list of licenses: http://hamsterdb.com/licensing/exceptions
I’m absolutely willing to add more licenses upon request.
Immediately after releasing 1.0.7, a user informed me of a weird behaviour which appeared after deleting database keys.
It took me about 20 hours to track it down… sometimes, when deleting a key (and it’s an extended key which does not fit into the index page and therefore was stored in an overflow area), the database page has to be merged with other pages because it’s getting too empty. And in one (rare, but nevertheless dangerous) case the overflow area was deleted, but there was still a key pointing to it. And from that moment on the index was in an inconsistent state.
Everything’s available for download.
1.0.7 is out! it fixes a bug on big-endian architectures - they were not able to open database files which were created on little-endian architectures.
From the README:
This release fixes a bug on big-endian architectures; Databases from little- endian architectures were not loaded correctly, and vice versa. A typo in the Tutorial was fixed.
Everything’s available for download.
Currently, it looks as if i stopped working on hamsterdb (and Ohloh’s “Decreasing year-over-year development activity“) really makes me feel bad!) - but that’s far from true. I spend every minute on hamsterdb2, the next generation. I will continue to maintain hamsterdb and i even hope that i have time to release a bugfix release today or even tomorrow.
As i wrote in an older blog entry, hamsterdb will focus on embedded devices with limited hardware; it will offer high configurability and a limited feature set, optimized on throughput and performance. (Therefore i currently do not plan to improve transaction support for hamsterdb).
In contrast, hamsterdb2 will be for modern (preferably multi-core) machines and modern applications. Here’s a list of buzzwords:
- multithreaded - hamsterdb2 will not be just threadsafe, but it will actively encourage the use of multiple threads. Performance intensive operations are processed in the background. Every API handle (for Environments, Databases and Transactions) can be used from multiple threads in parallel.
- transactional - hamsterdb2 will support ACID transactions and multiple isolation levels. Isolation levels can be set individually for each transaction. Transactions itself are kept in memory - whenever a Database is modified, the Database “diff” is stored in-memory; transaction conflicts are resolved in-memory, without disk access. Same applies to UNDO operations. Committed transactions are periodically flushed to disk in the background.
- logging/recovery: since transactions are kept in-memory, they are also written to a logical logfile. In case of a crash, all operations from this logfile are repeated. These operations are idempotent, which means that they can be applied multiple times without side effects. Incomplete/Active transactions are recreated (there’s an API function to enumerate all active transactions). The index file is based on a B+Tree with atomic algorithms and therefore does not need its own logfile.
- Simplified API - i think the API of hamsterdb was already quite simple to use. Nevertheless i managed to improve it a little bit.
- The current state? I’m currently working on the recovery algorithm. Transactions and the index files are already working, but the index files need improvements (they currently only work for fixed-size keys). There’s no freelist management yet - empty pages are not reused. And i only implemented the SERIALIZE isolation level - but others will be simple to do. Currently, there’s no support for duplicate keys, record numbers and cursors.
Feel free to post questions/comments!
The 1.0.6 release was overdue - my lack of time is a tribute to our baby, to the daily work, the preparations for moving to the new house and the beginning of a new hamsterdb version, which is a completely new library and will not share any code with the current architecture. Both libraries will coexist in parallel - hamsterdb is optimized for embedded architectures, the new hamsterdb will be optimized for concurrent access and transactions.
This release adds a new flag HAM_CACHE_UNLIMITED which uses unlimited cache, and is therefore nearly as fast as a pure In-Memory Database. Also, the unittests now compile with gcc 4.3.x and glibc 2.8. The C++ API has a new function to assign keys with a template parameter. ./configure has a new option –enable-system-zlib to link against -lz instead of the zlib version which is provided with hamsterdb. Finally, the tutorial has a new chapter about Transaction support.
Sources, CHANGELOG and precompiled win32 libraries are available for download here!
I just released hamsterdb 1.0.5!
From the README:
This release fixes several minor issues found by static code analysis tools. A
bug in the command line tool ham_dump was fixed. hamsterdb was ported to the
maemo.org SDK for ATMEL-based Nokia N810 cell phones. The C++ wrapper
now supports the Transaction API. On Linux, the flag O_NOATIME is specified
when opening or creating files. When closing the Environment or Database,
a pending Transaction can now be auto-committed (HAM_AUTO_COMMIT).
As always, grab it here: http://hamsterdb.com
hamsterdb 1.0.4 fixes a serious bug in the logging module. In an Environment with more than one Database, each Database had its own logging object - with the result that each of these objects overwrote stuff the other objects wrote, and the log became corrupted.
This bugfix somehow clouds the Real Big Thing - support for ACID Transactions! Being a fan of agile developmen, this release supports only a limited set of functionality; the biggest limitation is that there can be only one Transaction at a time.
I will try to fix these limitations one after the other.
Get the stuff here: www.hamsterdb.com.
Following yesterday’s python wrapper release, here are the wrappers for .NET and Java; both with support for Recovery and Logging.
Get them here: hamsterdb.com
Just a short note that i released the second version of the python wrapper - 0.0.2. it adds support for logging and recovery, which was introduced in hamsterdb 1.0.3.
As usual, get everything here: http://hamsterdb.com.
hamsterdb 1.0.3 adds support for logging and recovery. Both make hamsterdb even more fail-safe in case of a system crash or application crash. Logging can be enabled by specifying the flag HAM_ENABLE_RECOVERY.
I hope that i will soon have some time to write more about the recovery-implementation.
Download, Changelog and release notes can be found on hamsterdb.com.