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new 93aef61a BLOG - Pluggable Memtable Implementations in C* 4.1
93aef61a is described below
commit 93aef61a162c3074b284b096208c38964930baea
Author: Diogenese Topper <[email protected]>
AuthorDate: Thu Jul 21 16:53:28 2022 -0700
BLOG - Pluggable Memtable Implementations in C* 4.1
patch by Branimir Lambov, Chris Thornett, Diogenese Topper; reviewed by
Erick Ramirez for CASSANDRA-17761
Co-authored by: Branimir Lambov <[email protected]>
Co-authored by: Chris Thornett <[email protected]>
Co-authored by: Diogenese Topper <[email protected]>
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@@ -8,6 +8,31 @@ NOTES FOR CONTENT CREATORS
- Replace post tile, date, description and link to you post.
////
+//start card
+[openblock,card shadow relative test]
+----
+[openblock,card-header]
+------
+[discrete]
+=== Apache Cassandra 4.1 Features: Pluggable Memtable Implementations
+[discrete]
+==== July 21, 2022
+------
+[openblock,card-content]
+------
+Apache Cassandra 4.1 supports alternative memtable implementations. Learn more
about this feature and the proof of concept implementation included in the new
release.
+
+[openblock,card-btn card-btn--blog]
+--------
+
+[.btn.btn--alt]
+xref:blog/Apache-Cassandra-4.1-Features-Pluggable-Memtable-Implementations.adoc[Read
More]
+--------
+
+------
+----
+//end card
+
//start card
[openblock,card shadow relative test]
----
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+= Apache Cassandra 4.1 Features: Pluggable Memtable Implementations
+:page-layout: single-post
+:page-role: blog-post
+:page-post-date: July 21, 2022
+:page-post-author: Branimir Lambov
+:description: Pluggable Memtable Implementations in Apache Cassandra 4.1
+:keywords: apache cassandra, world party, cassandra world party, CWP, 2022,
schedule, moderator
+
+:!figure-caption:
+
+.Image credit: https://unsplash.com/@nevenkrcmarek[Neven Krcmarek^]
+image::blog/Apache-Cassandra-4.1-Features-Pluggable-Memtable-Implementations-unsplash-neven-krcmarek.jpg[Pluggable
Memtable Implementations]
+
+One of the new features of Apache Cassandra 4.1, introduced with enhancement
proposal #11 (https://cwiki.apache.org/confluence/x/0goBCw[CEP-11^]), is
support for alternative memtable implementations. This feature enables
developers to implement new memtable solutions and for users to select a
memtable implementation and configuration for each individual table in the
database.
+This is enabled by a new memtable option in `CREATE TABLE` and `ALTER TABLE`
statements that specifies the memtable configuration out of a set of options
defined in `cassandra.yaml`, for example:
+
+----
+CREATE TABLE heavy_use … WITH memtable = 'sharded';
+----
+
+where the `'sharded'` configuration is defined in `cassandra.yaml` as
+
+----
+Memtable:
+ Configurations:
+ Sharded:
+ class_name: ShardedSkipListMemtable
+ Parameters:
+ shards: 32
+ serialize_writes: false
+----
+
+Apache Cassandra 4.1 comes with only a proof-of-concept alternative memtable
implementation, which is a sharded skip-list solution that splits the memtable
into several shards that cover roughly the same portion of the token space
served by the node. This enables writes to different shards to apply
independently, without any congestion during modification of the data
structure, which is known to enable higher memtable performance for typical
Cassandra workloads. The example above shows h [...]
+
+* `shards` - the number of shards to split the memtable into.
+* `serialize_writes` - whether to lock the memtable shard during mutations.
+
+Locking is provided as an option. This avoids wasting processing time and
memtable space when multiple concurrent modifications prepare conflicting
mutations on the same partition during congested lock-free modification.
Locking will result in lower peak write throughput, but may improve the
longer-term sustained throughput because of storing slightly more information
in each flushed SSTable and giving more CPU time to compaction.
+The table below shows an example of the average throughput achieved while
writing 100GB of key-value data, with 10% reads, and with the given percentage
of skew, i.e., accesses hitting the same individual row.
+
+:!figure-caption:
+
+.[.small]#This test of average throughput uses
https://gist.github.com/blambov/00e8dbff5a97f321d30d0ef992465a08[the fallout
script which you can find here^].#
+image::blog/Apache-Cassandra-4.1-Features-Pluggable-Memtable-Implementations-graph.png[skip-list
graph]
+
+The project will be building on this feature and in the near future, the API
will be used to enable two exciting developments:
+
+* Intel’s persistent memory memtable
https://issues.apache.org/jira/browse/CASSANDRA-13981[(CASSANDRA-13981)^], a
memtable-only storage system promising extremely low latencies when suitable
hardware is used.
+* A Trie-based memtable
(https://cwiki.apache.org/confluence/x/kYuqCw[CEP-19^],
https://issues.apache.org/jira/browse/CASSANDRA-17240[CASSANDRA-17240^]), which
promises significant improvements in performance and garbage collection
overheads.
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