Expose Max Db Statement Size as a Config Option

[gingerwizard]

Currently the span.context.db.statement is limited to 10000 characters after which truncation occurs. This limit is easily exceeded on REST API based dbs that use JSON e.g. Elasticsearch. Proposal is to make this configurable similar tothe truncation limit for error messages.

[gingerwizard]

Note is particularly important when debugging requests to Elasticsearch from Kibana.

[trentm]

A temporary work around is to apply this patch to one's node_modules/elastic-apm-node/lib/config.js:

diff --git a/lib/config.js b/lib/config.js
index 38d6408..a5520b0 100644
--- a/lib/config.js
+++ b/lib/config.js
@@ -257,6 +257,8 @@ class Config {
           // Sanitize conf
           truncateKeywordsAt: config.INTAKE_STRING_MAX_SIZE,
           truncateErrorMessagesAt: conf.errorMessageMaxLength,
+          // XXX
+          truncateQueriesAt: 20000,
           // HTTP conf
           secretToken: conf.secretToken,

[trentm]

^^ proposing this for 7.13. Currently Dale is having "to maintain a fork for tests and any automation" for his es rally work.

[trentm]

Notes to self:

• perhaps do this together with changes to db.statement format for ES: Reconsider structure of context.db.statement #2019
• tracing-instrumentation-db.md spec says "We store up to 10000 Unicode characters per database statement." FWIW
• TODO: verify if >10k gets stored in ES docs or if apm-server clips or rejects. I don't (with a quick naive look) see clipping/length limiting in apm-server for this field.

[trentm]

@gingerwizard Once we publish an agent release with this change you'll be able to set the truncation limie for span.context.db.statement via the longFieldMaxLength: <number> config var. I try to post here again once we have that release.

[trentm]

@gingerwizard If it helps for https://github.com/elastic/rally-internal-tracks/issues/119 [email protected] has now been released that includes longFieldMaxLength to allow you to increase the max size for span.context.db.statement.