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Posted to notifications@couchdb.apache.org by GitBox <gi...@apache.org> on 2022/09/13 02:15:41 UTC
[GitHub] [couchdb] diachedelic opened a new issue, #4175: ES6 in view functions
diachedelic opened a new issue, #4175:
URL: https://github.com/apache/couchdb/issues/4175
I recently upgraded from CouchDB 1.6.1 to 3.2.2, and took a moment to clean up my view functions. In the following view function, all I did was change the `var` to a `let`:
function (doc) {
let start;
if (
doc._id.indexOf("geometries_") === 0 &&
doc.features.length > 0 &&
doc.parentID
) {
start = doc.features[0].geometry.coordinates;
if (typeof start[0] !== "number") {
start = start[0];
}
emit([0, start[0]], doc.parentID);
emit([1, start[1]], doc.parentID);
}
}
As a result, GET requests to this view began responding with an error:
```
{
error: 'killed',
reason: '{gen_server,call,\n' +
' [couch_index_server,\n' +
' {get_index,\n' +
' {couch_mrview_index,\n' +
' {mrst,\n' +
' <<174,230,212,124,70,180,183,172,250,90,95,225,147,32,152,1>>,\n' +
' nil,undefined,\n' +
' <<"shards/00000000-7fffffff/events_near_me_c3sc8-7r.1663034046">>,\n' +
' <<"_design/geometries">>,<<"javascript">>,[],false,\n' +
' {[]},\n' +
' [{mrview,0,0,0,\n' +
' [<<"by_parent">>],\n' +
' [],\n' +
' <<"function (doc) {\\n if (doc._id.indexOf(\\"geometries_\\") === 0) {\\n if (doc.parentID) {\\n emit(doc.parentID);\\n }\\n }\\n }">>,\n' +
' nil,[]},\n' +
' {mrview,1,0,0,\n' +
' [<<"location">>],\n' +
' [],\n' +
' <<"function (doc) {\\n let start;\\n if (\\n doc._id.indexOf(\\"geometries_\\") === 0 &&\\n doc.features.length > 0 &&\\n doc.parentID\\n ) {\\n start = doc.features[0].geometry.coordinates;\\n if (typeof start[0] !== \\"number\\") {\\n start = start[0];\\n }\\n emit([0, start[0]], doc.parentID);\\n emit([1, start[1]], doc.parentID);\\n }\\n }">>,\n' +
' nil,[]}],\n' +
' nil,0,0,undefined,undefined,undefined,undefined,undefined,\n' +
' nil},\n' +
' <<"shards/00000000-7fffffff/events_near_me_c3sc8-7r.1663034046">>,\n' +
' <<174,230,212,124,70,180,183,172,250,90,95,225,147,32,152,1>>}},\n' +
' infinity]}',
ref: 2175788010
}
```
Reverting to the `var` solves the issue. I have tested this both with a native MacOS installation and the official Docker image, with identical results.
Calling GET /_node/_local/_versions gives:
```
{
"javascript_engine": {
"version": "78",
"name": "spidermonkey"
},
....
}
```
From what I could discern, SpiderMonkey v78 was used in Firefox v78, which certainly supported the `let` statement. So shouldn't `let` be supported in view functions? Have I missed something?
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[GitHub] [couchdb] diachedelic commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
diachedelic commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1245015487
Oh, I found #2345, the PR for upgrading to SpiderMonkey 60 from 1.8.5. Something I still don't understand is why a view function like `function(doc) { ... }` ceased to be valid. It's just a function expression, why would that stop working with a newer version of SpiderMonkey? There is mention of a "new style" of view function, like `(function(doc) { ... });` but that makes even less sense to me, because it is an expression statement which does nothing.
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[GitHub] [couchdb] nickva commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
nickva commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1244859708
Ah no worries, thanks for reaching out.
There was an issue related to performance regression with custom reduces with later (> 1.8.5. spidermonkey) https://github.com/apache/couchdb/issues/3517.
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[GitHub] [couchdb] diachedelic commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
diachedelic commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1244872458
I was not using custom reducers, but the error certainly occurred more often when I used `let` instead of `var`. Perhaps that was just because `let` made SpiderMonkey work harder.
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[GitHub] [couchdb] diachedelic commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
diachedelic commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1245017685
Oh, I found https://issues.apache.org/jira/browse/COUCHDB-1643.
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[GitHub] [couchdb] nickva commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
nickva commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1244816446
@diachedelic I think it could be related to the transformation that happens in https://github.com/apache/couchdb/blob/main/share/server/60/rewrite_fun.js
There, we parse the javascript functions into an AST and patch the function to make turn "function(...) {...}" into a proper JS syntax (CouchDB global "function(...) {...}" it turns out are not valid JS). It could be that the parsers we use esprima and escogen don't handle ES6 syntax. That's just a guess so far, I haven't validated it yet.
A related issue perhaps as well: https://github.com/apache/couchdb/issues/2372
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[GitHub] [couchdb] diachedelic commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
diachedelic commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1244958916
Is there a way to profile CouchDB's execution of JavaScript? It would be interesting to know where the bottleneck is.
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[GitHub] [couchdb] diachedelic closed issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
diachedelic closed issue #4175: ES6 in view functions
URL: https://github.com/apache/couchdb/issues/4175
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[GitHub] [couchdb] nickva commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
nickva commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1244966200
couchjs processes are run as a pool so it maybe possible to compare the CPU usage of those couchjs processes before and after.
Or run a benchmark building a view on both setups and see which takes longer.
With the 2.x/3.x versions, setting the Q sharding factor could help parallelize view builds, so with Q=16 if you have a large database, all 16 shard ranges (and 3 copies if you have a 3 node cluster) will build in parallel.
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[GitHub] [couchdb] diachedelic commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
diachedelic commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1244852470
Sorry, I have mischaracterised this error. It appears to actually be a load-sensitive, intermittent failure that happened to correspond perfectly with me switching `var` and `let` a few times. I still don't understand why the error is occurring, but I don't think it is caused solely by using ES6 features in view functions.
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[GitHub] [couchdb] diachedelic commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
diachedelic commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1245002055
Thanks, that's good to know. If I run into unavoidable performance problems I will give it a shot.
Something else I would like to know is why the view functions need to be transpiled for newer SpiderMonkeys, but not for 1.8.5. Is there a discussion anywhere I can read more about this?
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[GitHub] [couchdb] nickva commented on issue #4175: ES6 in view functions
Posted by GitBox <gi...@apache.org>.
nickva commented on issue #4175:
URL: https://github.com/apache/couchdb/issues/4175#issuecomment-1244875316
That could be, it's hard to saw without more details metrics. That parser/emitter piece of code might have to work harder some newer code constructs like `let`.
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