Session.GetSessionSysVar returns nil for registered sysvars missing from the per-session map - #24530
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… map miss
Session.GetSessionSysVar previously returned interface{}(nil) when
ses.sesSysVars.Get(name) saw a map miss for a registered sysvar.
sesSysVars is a clone of the per-account snapshot from
mo_mysql_compatibility_mode; sysvars added to gSysVarsDefs without a
corresponding catalog row are absent from the cloned map, and Get
returns interface{}(nil) on map miss instead of the registered
Default. That violates MySQL `SELECT @@name` semantics (session value
> global default, never nil for a registered name) and breaks
downstream consumers like sub-Compiles spawned by CREATE TABLE CLONE
that try to read vector-index sysvars (ivf_threads_build,
kmeans_train_percent, ...) — they receive nil and either fail or
silently use zero values.
The function already had a wholesale-nil fallback (`if ses.sesSysVars
== nil { return gSysVarsDefs[name].Default }`); this commit extends it
to cover the per-key map-miss case, the realistic scenario for any
sysvar registered after the per-account snapshot was taken.
New TestGetSessionSysVar_MapMissFallsBackToDefault asserts both
`ivf_threads_build` (int64 default 0) and `kmeans_train_percent`
(float64 default 10) resolve correctly when the per-session map is
empty.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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XuPeng-SH
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May 21, 2026
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Reviewed the Session.GetSessionSysVar fallback change and the added regression test. The change is small, localized, consistent with the existing nil-session fallback behavior, and the focused frontend sysvar tests passed locally.
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…rom the per-session map (matrixorigin#24530) 1. Fix SystemVariables.Get to fall back internally. Broader scope (SystemVariables would need to know about gSysVarsDefs), but covers any direct caller of Get too. 2. Pre-populate sesSysVars at session creation by merging gSysVarsDefs defaults into the cloned account snapshot. Most principled — the per-session map becomes complete — but more invasive at session-init time. Going with the localized fix in GetSessionSysVar as the lowest-risk first step; options 1/2 can follow if the same nil-on-miss pattern bites other call sites. Tests TestGetSessionSysVar_MapMissFallsBackToDefault (pkg/frontend/authenticate_test.go) asserts the new fallback for ivf_threads_build (int64) and kmeans_train_percent (float64). Approved by: @XuPeng-SH
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What type of PR is this?
Which issue(s) this PR fixes:
issue #24529
What this PR does / why we need it:
Get too.
becomes complete — but more invasive at session-init time.
Going with the localized fix in GetSessionSysVar as the lowest-risk first step; options 1/2 can follow if the same nil-on-miss pattern bites other call
sites.
Tests
TestGetSessionSysVar_MapMissFallsBackToDefault (pkg/frontend/authenticate_test.go) asserts the new fallback for ivf_threads_build (int64) and
kmeans_train_percent (float64).