Ermia Save

ERMIA

Fast and Robust OLTP using Epoch-based Resource Management and Indirection Array

See our SIGMOD'16 paper [1] for a description of the system, our VLDBJ paper [2] for details in concurrency control, and our VLDB paper for replication.

[1] Kangnyeon Kim, Tianzheng Wang, Ryan Johnson and Ippokratis Pandis. ERMIA: Fast Memory-Optimized Database System for Heterogeneous Workloads. SIGMOD 2016.

[2] Tianzheng Wang, Ryan Johnson, Alan Fekete and Ippokratis Pandis. Efficiently making (almost) any concurrency control mechanism serializable. The VLDB Journal, Volume 26, Issue 4. 2017. preprint.

[3] Tianzheng Wang, Ryan Johnson and Ippokratis Pandis. Query Fresh: Log Shipping on Steroids. VLDB 2018.

Environment configurations

• Software dependencies: libnuma. Install from your favorite package manager. ERMIA uses mmap with MAP_HUGETLB to allocate huge pages. MAP_HUGETLB is available after Linux 2.6.32.
• Make sure you have enough huge pages. Almost all memory allocations come from the space carved out here. Assuming 2MB pages, the command below will allocate 40GB of memory:

sudo sh -c 'echo [x pages] > /proc/sys/vm/nr_hugepages'

This limits the maximum for --node-memory-gb to 10 for a 4-socket machine (see below).

• mlock limits. Add the following to /etc/security/limits.conf (replace "[user]" with your login):

[user] soft memlock unlimited
[user] hard memlock unlimited

Re-login to apply.

Adjust maximum concurrent workers

By default we support up to 256 cores. The limit can be adjusted by setting MAX_THREADS defined under config in dbcore/sm-config.h. MAX_THREADS must be a multiple of 64.

Build it

Currently the code only compiles with clang. We do not allow building in the source directory. Suppose we build in a separate directory:

$ mkdir build
$ cd build
$ CC=clang CXX=clang++ cmake ../ -DCMAKE_BUILD_TYPE=[Debug/Release/RelWithDebInfo]
$ make -jN

After make there will be three executables under build: ermia_SI that runs snapshot isolation (not serializable); ermia_SI_SSN that runs snapshot isolation + Serial Safety Net (serializable) ermia_SSI that runs serializable snapshot isolation *

• Serializable Isolation for Snapshot Databases, M. Cahill, U. Rohm, A. Fekete, SIGMOD 2008.

Run it

$run.sh \
       [executable] \
       [benchmark] \
       [scale-factor] \
       [num-threads] \
       [duration (seconds)] \
       "[other system-wide runtime options]" \
       "[other benchmark-specific runtime options]"`

System-wide runtime options

-node_memory_gb: how many GBs of memory to allocate per socket.

-null_log_device: flush log buffer to /dev/null. With more than 30 threads, log flush (even to tmpfs) can easily become a bottleneck because of a mutex in the kernel held during the flush. This option does not disable logging, but it voids the ability to recover.

-tmpfs_dir: location of the log buffer's mmap file. Default: /tmpfs/.

-enable_gc: turn on garbage collection. Currently there is only one GC thread.

-enable_chkpt: enable checkpointing.

-phantom_prot: enable phantom protection.

-warm-up: strategy to load versions upon recovery. Candidates are:

• eager: load all latest versions during recovery, so the database is fully in-memory when it starts to process new transactions;
• lazy: start a thread to load versions in the background after recovery, so the database is partially in-memory when it starts to process new transactions.
• none: load versions on-demand upon access.

SSI and SSN specific:

--safesnap: enable safe snapshot for read-only transactions.

SSN-specific:

--ssn-read-opt-threshold: versions that are read by a read-mostly transaction and older than this value are considered "old" and will not be tracked; setting it to 0 will skip all read tracking for read-mostly transactions (TXN_FLAG_READ_MOSTLY).

SSI-specific: --ssi-read-only-opt: enable P&G style read-only optimization for SSI.