PBXT version 0.9.5 has been released and can be downloaded from
This version includes a number of major structural changes to the
implementation in order to improve performance. In addition, all bugs
reported so far have been fixed. For further information on this
release, please read my blog, http://pbxt.blogspot.com, and the
associated comments. Details of all changes made are given in the
release notes below.
PrimeBase XT (PBXT) is a new transactional database engine for MySQL.
It has been designed for modern, web-based, high concurrency
environments. The Beta release of PBXT is planned for September 2006.
The current version is based on MySQL 4.1.16 and runs on Mac OS X and
Linux. The next version will include support for the new 5.1 storage
engine API and 64-bit processors.
Any questions, comments and bug reports can be sent directly to me.
Thanks for your support!
SNAP Innovation GmbH
PBXT Release Notes
------- 0.9.5 - 2006-07-03
RN15: This version concludes the re-structuring of the PBXT
implementation. I have made a number of major changes, including:
- All files except the transaction logs are now associated with a
particular table. All table related files begin with the name of the
table. The extension indicates the function.
- I have merged the handle and the fixed length row data for
- Only the variable size component of a row is stored in the data log
files. As a result the data logs can now be considered as a type of
- Memory mapped files are no longer used because it is not possible to
flush changes to the disk.
RN14: File names have the following forms:
[table-name]-[table-id].xtr - These files contains the table row
pointers. Each row pointer occupies 8 bytes and refers to a list of
records. The file name also contains the table ID. This is a unique
number which is used internally by XT to identify the table.
[table-name].xtd - This file contains the fixed length data of a table.
Each data item includes a handle and a record. The handle references a
record in the data log file if the table contains variable length
[table-name].xti - This file contains the index data of the table.
[table-name]-[log-id].xtl - This is a data log file. It contains the
variable length data of the table. A table may have any number of data
log files, each with a unique ID.
xtlog-[log-id].xt - These files are the transaction logs. Log entries
that specify updates reference a data file record. Each active thread
has its own transaction log in order to avoid contension.
RN13: Fixed the bug "Hang on DROP DATABASE". [RESOLVED: 0016]
RN12: PBXT currently only supports the "Serializable" transaction
isolation level. This is the highest isolation level possible and
includes the "repeatable-read" functionality [RESOLVED: 0015]. This is
implemented by giving every transaction a snapshot of the database at
the point when the transaction is started.
If the transaction tries to update a record that was updated by some
other transaction after the snapshot was taken, a locked error is
returned. A deadlock can occur if 2 transactions update the same record
in a different order. PBXT can detect all deadlocks.
RN11: I have implemented write buffering on the table data files.
RN10: The unique constraint (UNIQUE INDEX/PRIMARY KEY) is now checked
correctly. [RESOLVED: 0008]
RN9: I have implemented a conventional B-tree algorithm for the indices
(instead of the Lehman and Yoa B*-link tree). Although this reduces
concurrency it improves the performance of queries significantly
because of the simplicity of the algorithm. Deletion is also
implemented in a very simple manner. [RESOLVED: 0007]
RN8: PBXT now has only 2 caches [RESOLVED: 0006]:
The Index Cache (pbxt_index_cache_size): This is the amount of memory
the PBXT storage engine uses to cache index data and row pointers. This
is all the data in the files with the extensions '.xti' and '.xtr'.
This cache is managed in blocks of 2K.
The Record Cache (pbxt_record_cache_size): This is the amount of memory
the PBXT storage engine uses to cache table row data (handles and
records). This is all the data in the files with the extension '.xtd'.
The size of the caches are determined by the values of the system
variables pbxt_index_cache_size and pbxt_row_cache_size. By default
these values are set to 32MB.
RN7: Auto-increment is now implemented in memory. This is done by doing
a MAX() select when a table is first opened to get the high value.
After that, then high value is incremented in memory on INSERT. On
UPDATE (or INSERT) the value in memory is adjusted if necessary. This
method also makes it possible for rows to be inserted simultaneously on
the same table. [RESOLVED: 0005, 0014]
RN6: ./run-all-tests --create-options=TYPE=PBXT succeeds. [RESOLVED:
RN5: Using sql-bench and my own Java based test I have confirmed that
PBXT behaves correctly during multi-threaded access. [PARTIALY
RN4: Load/Stability test. Using sql-bench I have tested PBXT under load
over a long period of time. [PARTIALY RESOLVED: 0001]
------- 0.9.2 - 2006-04-01
RN3: Fixed a bug that cause the error "-6: Handle is out of range:
RN2: Implemented SET, ENUM and YEAR data types.
RN1: Fixed a bug in the error reporting when a table is created with a
datatype that is not supported. [RESOLVED: 0011]