[SOLR-14931] Macros in appends/invariants parameters not getting expanded in Solrcloud

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 7.6, 8.6.3
• Component/s: SolrCloud
• Assignee: Unassigned
• Reporter: Johannes Baiter
• Created: 14/Oct/20 09:36
• Updated: 13/Feb/21 00:08

Description

Macros in a request handler's appends or invariants parameter sets are not getting expanded when running in a SolrCloud setup.

In my case, I have a handler like the following:

<requestHandler name="/myhandler" class="solr.SearchHandler">
  <lst name="defaults">
    <str name="q">some_field:"$${my_term}"</str>
    <str name="fl">term_defaults:'$${my_term},freq_defaults:docfreq(some_field, '$${my_term}')</str>
  </lst>
  <lst name="appends">
    <str name="fl">term_appends:'$${my_term}',freq_appends:docfreq(some_field, '$${my_term}')</str>
  </lst>
</requestHandler>

When querying the handler with `?my_term=foobar&echoParams=all`, something like this is the result:

{
    "response": {
        "docs": [
            {
                "term_defaults": "foobar",
                "term_appends": "${my_term}",
                "freq_appends": 0,
                "freq_defaults": 1
            }
        ],
        "maxScore": 13.244947,
        "numFound": 1,
        "start": 0
    },
    "responseHeader": {
        "QTime": 262091,
        "params": {
            "echoParams": "all",
            "fl": [
                "term_defaults:'foobar',freq_defaults:docfreq(some_field, 'foobar')",
                "term_appends:'foobar',freq_appends:docfreq(some_field, 'foobar')"
            ],
            "my_term": "foobar",
            "q": "some_field:\"foobar\"",
            "rows": "1"
        },
        "status": 0,
        "zkConnected": true
    }
}

As you can see, the macro in the appends fl parameter gets expanded in the responseHeader.params.fl field, but not in the actual document.

I believe the reason for this is the following:

• Setting of defaults/invariants/appends happens once before the request gets sent to the shards
• Here, macro expansion happens, i.e. the shards get the fully expanded parameters
• On the shards, once again, defaults/invariants/appends are set (https://github.com/apache/lucene-solr/blob/master/solr/core/src/java/org/apache/solr/handler/RequestHandlerBase.java#L209)
• However, this time macros are not expanded (https://github.com/apache/lucene-solr/blob/master/solr/core/src/java/org/apache/solr/request/json/RequestUtil.java#L151-L161)
• For defaults parameters, this doesn't break anything, since the (expanded) parameter from the request takes precedence over the server-supplied value.
• However, for appends, both the expanded and the unexpanded version are now set, while for invariants the expanded value is removed from the params

I think the easy/obvious fix for this would be not to set defaults/invariants/appends parameters twice, i.e. disable it when isShard=true, just like macro expansion, but I don't have the full picture if that might not break something else.

Here's the Twitter thread where I rubber-ducked through this issue: https://twitter.com/jbaiter_/status/1316023733576843272

Issue Links

• relates to: SOLR-10059 In SolrCloud, every fq added via <lst name="appends"> is computed twice.