The final version means that there is unlikely to be any more major development in the system. There may be some bug fixes H-Store in the years that follow, but you should not expect any new features or projects. There will probably be one or two more H-Store papers published this year as well. If you want to use a more state-of-the-art DBMS that is based on H-Store’s architecture, then you should use VoltDB. Yes, VoltDB is open-source. Stop asking. There is also the S-Store project that is adding support for in-memory stream processing on top of the H-Store architecture.

So this is the end. All of the project’s papers, presentations, and posters are available on the publications page. We would like to thank the many students, collaborators, and friends that have helped us over the last eight years.

Some of us are also now building the next system…

Major highlights of this release:

1. Improved the anti-caching architecture in the system to be smarter about moving in and out of secondary storage. This includes the use of a CountMin Sketch to selectively merge a cold data block back into memory if the data is accessed a lot in a window. There is also support for multi-tier anti-caching to allow you to define a hierarchical storage layout for spilling tuples from DRAM to durable storage. [8d19ab1] [b654e8b] [063e024] [4fb3757] [ee2301b] [d87cefe]
2. Added support for tuple-level eviction and retrieval when using non-volatile memory (NVM). Instead of using tombstones, evicted tuples are moved to a separate pool that is stored on NVM. All of the operator executors can then access these tuples directly without needing abort and restart the txn. [ab56f88] [37b3638] [074da8d]
3. The default index data structure for H-Store is the stx::btree. This improves throughput for single-partition workloads by about 10% while also reducing memory consumption. [87465c6]
4. Added support for the new compressed OLTP hybrid indexes. See our SIGMOD’16 paper for more information. [3c10031]
5. Added new AntiCacheStatsSource to retrieve additional information about the evicted tuple storage. [e1bca3b]
6. FIX: Removed a race condition involving the EE’s shared buffer and the AntiCacheEvictionManager. This problem occured when the anti-caching subsystem evicts tuples and a transactions accesses an EvictedTuple. The EE would then lose the information about the tuple accessed. [90efa79]
7. FIX: Long-existing memory leak in the EE’s undo log. This was embarrassing. [f77f8d0]
8. FIX: The EE’s IndexStats now store memory information correctly for tables with multiple indexes. [78aff6f] [29527be]
9. FIX: The EE’s AntiCacheManager was using inaccurate stats when deciding how much data to evict, which would then cause it to write out empty blocks of data. [17fe61d]

This release can be downloaded via Github:

• Source Code: https://github.com/apavlo/h-store/tree/release-2016-06
• Tarball: https://github.com/apavlo/h-store/tarball/release-2016-06

Major highlights of this release:

1. Re-factored anti-cache code in the EE to make it more extensible. On-disk blocks now support tuples from multiple tables. [6e5e320] [f03faf6] [5c11737] [23025d2]
2. New anti-cache storage back-end designed specifically for non-volatile memory. [4e007db] [b9b2a68] [8cf939d] [34aabbe]
3. Anti-caching rollbacks now supports multi-partition transactions. [13539d0] [4fdf0cf] [ba759a5] [d3c5ee1]
4. Ported experimental ARIES implementation from Nirmesh Malviya’s VoltDB code. This is from his ICDE 2014 paper. [0936955] [f7be730] [53ea2b9] [2a37256]
5. Added new ARTICLES benchmark. This workload simulates users posting content and comments on a news aggregation website like Reddit/HackerNews. [5b2abf1] [a299082]
6. FIX: H-Store now supports gcc 4.8. [d0ae5e3]
7. FIX: Restored support for snapshots creation and loading. [23cfb02] [2d16006]
8. FIX: Simplified materialized views were not initialized properly. [7346860]

This release can be downloaded via Github:

• Source Code: https://github.com/apavlo/h-store/tree/release-2014-05
• Tarball: https://github.com/apavlo/h-store/tarball/release-2014-05

We are also excited to announce the start of new research projects in H-Store with our new collaborators at Intel Labs as part of the ISTC for Big Data and at the Qatar Computing Research Institute. More information on these projects will be available later in the winter.

Major highlights of this release:

1. Improved speculative transaction execution. H-Store now supports optimistic concurrency control for speculative tasks using a new tuple-level read/write tracking mechanism. The PartitionExecutor now uses a new conflict checking API that can determine whether it is safe to speculatively execute a transaction before it is invoked or during the PREPARE phase of 2PC. [a2e3e09] [5b94e06] [3ea53e8] [5dbfa36] [b2fa101]
2. New automatic query prefetching for distributed transactions. The system can identify when a transaction will need to execute a query at a remote partition before it queued up and then piggyback that query invocation in the initialization request. These queries will be asynchronously executed and have their results returned to the base partition to avoid needing to have the transaction block waiting for the network roundtrip. [859972b] [3bc4fbe] [51cf9d8] [e737233]
3. Various performance improvements and optimizations for the anti-caching feature, including support for updating the internal LRU chain for tuples accessed through secondary indexes. [e33d394]
4. Added support for Mac OSX 10.7. [5c64bd9] [b6714a9]
5. New Benchmarks: Added the SmallBank benchmark from Mohammad Alomari and Michael Cahill. [475bcd1] [1773453] [edccaa0]
6. FIX: The “early prepare” optimization for 2PC has been broken for some time. It was finally fixed in exchange for Aaron giving Andy a non-sensual massage at SIGMOD. [6d655dc] [151802b]
7. FIX: Fixed support in the for queries using constant values. This prevents them from having to be broadcast to every partition. Query predicates that use a equality comparison with a constant value are now routed to the correct number of partitions. Non-equality predicates are broadcast to every partition. [6c7c911] [81b0f02]
8. FIX: INSERT/UPDATE/DELETE queries on replicated tables now return the logical number of tuples modified. [f230114]

This release can be downloaded via Github:

• Source Code: https://github.com/apavlo/h-store/tarball/release-2013-11
• Tarball: https://github.com/apavlo/h-store/tarball/release-2013-11

Like sands through the hourglass, so are the days of our lives. And with that, the H-Store project is pleased to announce the release of the latest version of its high-performance, distributed transaction processing database management system. This version contains a significant new advancement in main memory NewSQL systems called anti-caching. H-Store now includes a disk-resident, block storage anti-cache to store “cold” data that has been removed from the memory-resident storage in order to free up space for new data. Preliminary experiments show that H-Store with anti-caching outperforms traditional DBMSs even for databases that are larger than the amount of memory available on a single node.

If the amount of memory used in the partitions for an HStoreSite goes above an administrator-defined threshold, then H-Store will evict the least recently used tuples and write them out to the anti-cache storage disk. H-Store still maintains index information in memory for any evicted tuples stored on disk. If a transaction attempts to access one of these evicted tuples, then it is switched into a “pre-pass” mode where the engine records all tuples that it tried to access. Once that transaction attempts to do something with those tuples (e.g., modify them, return them to the stored procedure), then it is aborted and put in a queue while the AntiCacheManager thread asynchronously retrieves those records and merge them back into memory.

Additional information about the new anti-caching architecture in H-Store is available on-line:

• Anti-Caching and Non-Volatile Memory for Transactional DBMSs (Pavlo / Stonebraker)
• The Traditional Wisdom is All Wrong (DeBrabant)

Major highlights of this release:

1. New anti-caching feature allows H-Store to support databases that are larger than the amount of memory available to an HStoreSite. This initial implementation uses BerkeleyDB’s hash table (which is now included in the source code).
2. Improved H-Store’s built-in implementation of the YCSB benchmark. The data generator is now multi-threaded and the transactions are guaranteed to be deterministic. [2ec227a] [7302cd8] [5747a41] [9791e1d]
3. Improved runtime performance of command logging. The PartitionExecutors will now send completed transactions to the TransactionPostProcessor threads. This helps to reduce the latency of transactions. [9d66da2] [88550be] [1292376] [3b13cd4]
4. Reduced the number of TransactionCleaner threads needed to clean-up finished transactions and return them to internal object pools. [844db91]
5. Various performance optimizations and stability fixes. [fb81eb9] [5b15079] [8de21a6] [2895a38] [4a12097] [2fa67a0] [923e155] [831ab1c] [06e8144] [7ee989d]

The source code for this release can be downloaded via Github:

https://github.com/apavlo/h-store/tarball/release-2013-04

The H-Store project is pleased to announce the release of the latest version of its high-performance, distributed OLTP database management system. This version consists of mostly stability, performance, and memory improvements. New features include more aggressive speculative execution of single-partition transactions, improved internal statistics gathering and reporting for benchmarks. We have also added over 200 new test cases for H-Store. As a result, this release is dedicated to the memory of Aaron Elmore.

The next release in early 2013 will contain significant new research features.

Major highlights of this release:

1. Rewrote incoming network request processing, transaction queue processing, and execution flow path. This greatly improves the performance of a single HStoreSite on multi-core nodes, reduces the amount of memory used by each HStoreSite instance, and improves server-side connection throttling. [54e2df0] [668e7d5] [bcc481f] [ce0d3fd]
2. Improved performance of command logging (i.e., op log) and fixed a rare dead-lock problem. [0e9c385d] [cff105d] [0e9c385]
3. Integrated new Speculative Execution Scheduler to find non-conflicting transactions to execute whenever a distributed transaction is stalled at a partition. The project compiler now automatically computes the read-write and write-write conflicts between the queries in each stored procedure. [68576a3] [6795bb2]
4. Mispredicted transactions do not count queries against replicated tables or secondary indexes when computing which partition to redirect the transaction request. This makes the TM1/TATP benchmark entirely single-partitioned and greatly improves performance. [9a9ef76b]
5. Added the ability to enable/disable JVM asserts for either the database cluster nodes or the benchmark framework using the new site.jvm_asserts and client.jvm_asserts parameters. [f21a8f6]
6. New client-side benchmark result output options. This allows the BenchmarkFramework to automatically retrieve CSV files from H-Store’s internal statistics catalog. [08d310a] [52ab623] [1038ded] [f47ebff]
7. New @GetConfiguration and @SetConfiguration system procedures to retrieve/manipulate HStoreConf parameters at run time. [cae1f0a] [ab4f5c0]
8. The default version of the JVM used in H-Store is now Java 1.7. This fixes a bug in Java 1.6 where the transaction prediction models that causes the JVM to SIGSEV. [945f590] [5b7f6a79].

The source code for this release can be downloaded via Github:

https://github.com/apavlo/h-store/tarball/release-2012-12

Major highlights of this release:

1. New Feature: Added new command logger that can write out successfully executed transactions to a log file at each node. The logger uses a separate thread and group commits transactions with minimum overhead to throughput. This log can then be replayed for recovery (work in progress). [ceb6a49] [ae4c82b] [abdc371] [99ffc9f] [d53afcc]
2. New Feature: Defer the execution of queries in single-partition transactions until a later point in time when the partition’s execution thread is idle. [8037dfe]
3. New Feature: Added support for ad-hoc queries. This allows you to execute single queries that are not part of a stored procedure. The H-Store distribution also provides a command-line terminal to connect to an H-Store cluster. [faf297c] [fda4c41]
4. New Benchmarks: VoltDB’s voter benchmark, Wikipedia, Yahoo!’s ycsb benchmark, and TPC-E (per David DeWitt’s persistent request). [5992d22] [0caa40c] [9cc5895] [#68]
5. Complete overhaul of the server-side infrastructure from processing incoming transaction requests from clients. This great improves scalability for workloads with very short single-partition transactions on machines with many cores (>10). [d03ba80]
6. Optimized and improve client side execution in benchmark framework. Reduced CPU overhead of each client thread. Added support for multiple JVM instances per client host. Added ability to specify whether client threads share a connection to the database cluster. [9f3c2d62] [df150881] [e44b3314]
7. Improve query plan optimization for distributed OLAP-style queries [e889abb] [89d06c8]
8. Major refactoring of the source code repository: all of the benchmark code has been moved in src/benchmarks. [a321847]

The source code for this release can be downloaded via Github:

https://github.com/apavlo/h-store/tarball/release-2012-06

Major highlights of this release:

1. Significant speed optimizations for single-partition transactions. [cf9be4a] [c67babd] [f2659fd] [0425253] [243f99d] [5abd178]
2. Fixed several memory leaks for aborted/read-only transactions. [ddf2f23] [e429821]
3. Fixed several stability issues when transactions share lock-free data structures [4956be9]
4. Fixed predicate/aggregate pushdowns for distributed query plans [4956be9] [31eff68]
5. Restored the ability for transactions to return the proper status codes on failures that mimic VoltDB’s protocol. [ae4a6a4] [f374d49]
6. H-Store’s Fabric automatic deployment script for EC2 now supports multiple concurrent “virtual” clusters. This allows you to easily assign instances to independent clusters under a single AWS account. [1202f4e]
7. Restored preliminary support for VoltDB’s regression test suite. [1f4f465] [c434fa2] [1945aba0]
8. Fixed building on OS X Lion [0328973]

The source code for this release can be downloaded via Github:

https://github.com/apavlo/h-store/tarball/release-2012-03

Important: The major change in this release is that the source code repository has been moved entirely to Github. The original Subversion will remain online for the time being but all new features and fixes will be in Github.

This latest release includes several performance optimizations for both single-partition and distributed transactions, as well as support for new features, such as MapReduce transactions.

Major highlights of this release:

1. Complete re-write of the distributed transaction coordination protocol. H-Store no longer uses the centralized Canadian-style transaction coordinator and instead uses a VoltDB-style timestamp-based ordering protocol (r2365, r2366)
2. When the database cluster is brought online, the HStoreCoordinator at each node will use an NTP-style algorithm to estimate the clock skew between all other nodes. It will then offset its internal logical clock used when generating globally unique transaction ids to minimize the discrepency between nodes. This improves throughput for distributed transactions on large deployments using Amazon EC2. (r2609)
3. The clients in H-Store’s built-in benchmark framework are now multi-threaded. The client.processesperclient parameter now specifies the number of client threads to use per JVM. This has been tested to scale to thousands of threads per JVM. (r2429, r2430)
4. Restored support for VoltDB’s bingo benchmark (r2534, r2535). Renamed the expanded Airline benchmark to SEATS (r2572)
5. Removed unused object pool pre-loading configuration parameters. (r2406)
6. Various improvements to reduce to amount of memory used store the internal state of transactions in the system. (r2379, r2377, r2376)

The source code for this release can be downloaded via Github:

https://github.com/apavlo/h-store/tarball/release-2012-01

Major highlights of this release:

1. The BatchPlanner can now quickly determine whether a query batch will execute entirely on the local partition and will use a cached batch plan if it is. This provides a significant speed improvement for single-partition transactions. (r2343, r2344)
2. Added the ability to pin the ExecutionSite’s Java thread to a fixed number of cores (using taskset). All other HStoreSite threads are only allowed to execute on the remaining CPU cores. See the ${site.cpu_affinity} parameter documentation for more information. (r2339)
3. New parameter ${client.txn_hints} that allows clients to route transaction requests to the proper node in the cluster, thereby reducing two extra network hops. (r2312, r2313)
4. Fixed automatic distribution of vertically partitioned tables when using the @LoadMultipartitionTable sysproc. (r2317)
5. Fixed hstore-benchmark so that it exits with a non-zero status code when the benchmark fails to execute to completion. (r2266)
6. H-Store now includes an automatic deployment script for Amazon EC2 based on Fabric and Boto. More information can be found here.

The source code for this release can be downloaded via anonymous SVN:

https://database.cs.brown.edu/svn/hstore/tags/release-2011-09

Major highlights of this release:

1. Improved speculative execution of single-partition transactions. All transactions can be speculatively executed whenever a multi-partition is blocking waiting to be executed. Use the site.exec_speculative_execution configuration to enable. (r2137, r2145, r2192)
2. New TransactionEstimator can automatically determine whether a transaction is single-partition at runtime. Distributed transactions are executed with the minimum number of partitions. Alternatively, you can use site.exec_force_singlepartitioned to force all transactions to execute as single-partitioned, and any mistakes are automatically rolled back and restarted as multi-partitioned.
3. Fixed concurrency/synchronization issues in ProtoRpcChannel/Server and VoltProcedureListener for write available callbacks. (r2183, r2155). Fixed synchronization issues for MarkovPathEstimator and TransactionEstimator (r2198)
4. Can now configure output directories for HStoreSite, Dtxn.Coordinator, and Client log files.
5. All node.* configuration parameters have been renamed to site.*.
6. Fixed a race condition when the middle PlanFragment for three-way joins would not get queued up for all partitions at the same time. This would cause the Dtxn.Coordinator to halt. (r2127)
7. Reduced JUnit test time by allowing each test case in a single JVM invocation to reuse benchmark project jar files. (r2139)

The source code for this release can be download via anonymous SVN:

https://database.cs.brown.edu/svn/hstore/tags/release-2011-07

Note also that the supplemental resource files (e.g., sample workload trace logs) have been moved out of the source code repository into a separate external repository:

https://database.cs.brown.edu/svn/hstore-files/