Mongodb ARM64 support explanation from Michael Hudson-Doyle.
1) MongoDB uses JS for two things:
i) The 'mongo' shell that people use for interactive use and admin
tasks etc. This is perhaps not used so much in production, but
it's something that most people use when first learning about
mongo, e.g. it's the very first command in the getting started
doc:
http://docs.mongodb.org/manual/tutorial/getting-started/
ii) A few server side scripting functions -- writing queries in js
and the map/reduce stuff. These are considered a bit esoteric
and most people probably don't actually use them but of course
some do.
2) MongoDB 2.4 (the version in trusty) ships with two javascript
engines: spidermonkey and v8. There is some license incompatibility
with spidermonkey such that mongo said we'd be breaking the law if we
distributed binaries built with it. The version of v8 that is used
by mongodb 2.4 does not work on arm64.
3) MongoDB 2.6 removed the spidermonkey js engine.
4) Soon after 2.6 was released, mongodb did the work to add another js
engine: one for a version of v8 that does work on arm64.
5) Unfortunately, this version of v8 handles OOM by calling abort() --
which is not a problem for the shell really but a very bad thing for
the server side scripting functions, as a single query using too much
RAM shouldn't cause the database daemon to abort.
6) MongoDB 2.6 is the version in utopic. For some reason, it is built
for arm64 but with scripting disabled, which means that the shell
just segfaults on startup. This is clearly not ideal.
7) I built packages in a PPA:
https://launchpad.net/~mongodb-arm64/+archive/ubuntu/ppa
that backport the support for the newer v8 js engine (and because
this newer v8 version isn't packaged yet, it has the new version of
v8 in a 20 megabyte distro patch).
Many thanks Michael for such a clear explanation.
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https://bugs.launchpad.net/bugs/1381967
Title:
mongodb shell crash on arm64
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