instance-performance-triage

Instance Performance Triage

Two questions arrive constantly and both have the same wrong answer: "the instance is slow" and "my nightly job never ran". The wrong answer is to write a GlideRecord sweep and run it through snow_execute_script. On an instance that is already struggling you have just added a transaction, and whatever you measure includes yourself. The platform already records what you need. Read it.

This guide is about reading it correctly, because most of the failure modes here are silent — you get a plausible-looking answer that is not an answer.

Rule zero: a wrong field name returns everything

The Table API does not reject an encoded query that references a column the table does not have. It drops the condition, logs Invalid query detected / Unknown field <x> in table <y> to syslog, and returns rows up to sysparm_limit. Same for sysparm_fields: unknown names are simply absent from the result, so a tool that maps them produces undefined, and a tool that counts them produces zero.

The two consequences you must hold in your head for the whole of this guide:

• A full result set does not mean your filter matched. It may mean your filter evaporated.
• An empty result set does not mean the instance is healthy. It may mean the table is not readable by the service account, or the rows were flushed, or you filtered on a value the column never holds.

So before you filter on any column named in this guide, on your instance, confirm it exists:

await snow_discover_table_fields({ table_name: "sys_trigger" })

The table-api-reads skill covers this same behaviour from the read-tool side; what follows is the part you need in front of you while reading telemetry.

One catch: that tool queries sys_dictionary with name=<table>, which returns only the columns defined on that table, not inherited ones. sysauto_script defines very little of its own — the scheduling columns live on its parent sysauto — so a lookup against the child alone under-reports what you can actually filter on. When a table extends another, query the dictionary for the whole chain: