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[FDC] Fix the transaction hang bug with pglite #9771

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fredzqm merged 4 commits into from
Jan 21, 2026
Merged

[FDC] Fix the transaction hang bug with pglite #9771

fredzqm merged 4 commits into from
Jan 21, 2026
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@fredzqm fredzqm commented Jan 21, 2026 •
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Description

Fix #9756

Before v15.2.1, FDC emulator uses prepared statement with pglite.

pglite has numerous limitations & bugs with prepared statement protocol. (Refer to electric-sql/pglite#223)

  • If an invalid SQL statement is prepared with pglite, its response crash the *sql.DB driver.
  • If there are multiple prepared statements, the prepared statement are mixed up.
    We ended up adding a maxOpenConnections: 1 to work around it.
    With prepared statement, all queries are routed to the same connection.

At v15.3.0, FDC switched to avoid prepared statement with pglite, hoping to get around pglite limitations.

  • It properly returns "pg error message" for any invalid SQL. Essential for direct SQL launch.
  • However, without prepared statement, *sql.DB.Begin() tries to spin up a new connection and get stuck due to maxOpenConnections: 1.

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gemini-code-assist bot commented Jan 21, 2026

Summary of Changes

Hello @fredzqm, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical bug where the Data Connect emulator would hang during transactions when using PGlite. The fix involves an internal change to how the emulator interacts with PGlite, specifically by removing a previous limitation on the number of open connections. This change ensures smoother and more reliable operation of the Data Connect emulator with PGlite by allowing multiple concurrent connections now that prepared statements are no longer an issue.

Highlights

  • PGlite Transaction Hang Fix: This PR resolves a transaction hang bug in the Data Connect emulator when interacting with PGlite by modifying how database connections are managed.
  • PGlite Connection Limit Removal: The maxOpenConnections: 1 limit for PGlite connections in the Data Connect emulator has been removed. This is now possible because the emulator has been updated to avoid prepared statements, which previously necessitated the single-connection restriction.

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Code Review

This pull request fixes a transaction hang bug in the Data Connect emulator when using PGlite by allowing multiple connections. The change removes the maxOpenConnections: 1 setting, and the rationale is well-documented in a comment. My review includes a suggestion to improve code readability by relocating this comment.

@fredzqm fredzqm requested a review from joehan January 21, 2026 05:05
@fredzqm fredzqm merged commit ac7ca0b into main Jan 21, 2026
46 of 47 checks passed
@fredzqm fredzqm deleted the fz/txn-pglite branch January 21, 2026 15:36
MichaelDoyle pushed a commit that referenced this pull request Jan 22, 2026
@fredzqm @MichaelDoyle
[FDC] Fix the transaction hang bug with pglite (#9771)
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@joehan joehan joehan approved these changes

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Successfully merging this pull request may close these issues.

Data Connect Emulator v3.0.2 Transaction Mutation Hang

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