Stack overflow when parsing script with thousands of UNIONs

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#49 opened on Jul 24, 2023 5 comments 1 reaction 0 assignees View on GitHub

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Assessment

Difficulty: 4/5
Estimated time: 3-5 days
Newbie friendliness: 32/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Stale
Tech stack: sql
Domain: compilers, databases

Research direction

Start by reproducing the overflow with a large SQL file containing thousands of UNIONs and inspect the TSqlParser, TSqlFragmentVisitor, and BinaryQueryExpression call path shown in the stack trace. The work is done when these inputs parse without stack overflow and visitor behavior remains intact.

Written by the indexing model from the issue text.

Description

TSqlParser results in a stack overflow exception when parsing large SQL files containing a lot of UNIONs (example: in a view or stored procedure). Culprit is likely the recursive visitor pattern, changing it to iterative may fix the issue.

Stack trace:

Microsoft.SqlServer.TransactSql.ScriptDom.TSqlFragmentVisitor.Visit(Microsoft.SqlServer.TransactSql.ScriptDom.BinaryQueryExpression)
Microsoft.SqlServer.TransactSql.ScriptDom.TSqlFragmentVisitor.ExplicitVisit(Microsoft.SqlServer.TransactSql.ScriptDom.BinaryQueryExpression)
Microsoft.SqlServer.TransactSql.ScriptDom.BinaryQueryExpression.Accept(Microsoft.SqlServer.TransactSql.ScriptDom.TSqlFragmentVisitor)
Microsoft.SqlServer.TransactSql.ScriptDom.BinaryQueryExpression.AcceptChildren(Microsoft.SqlServer.TransactSql.ScriptDom.TSqlFragmentVisitor)
Microsoft.SqlServer.TransactSql.ScriptDom.BinaryQueryExpression.Accept(Microsoft.SqlServer.TransactSql.ScriptDom.TSqlFragmentVisitor)
Microsoft.SqlServer.TransactSql.ScriptDom.BinaryQueryExpression.AcceptChildren(Microsoft.SqlServer.TransactSql.ScriptDom.TSqlFragmentVisitor)

Dominant language: GAP
Stars: 277
Forks: 43
Avg merge: 6d 17h
Merged PRs (30d): 3

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