go-sql-driver/mysql

Return useful error when attempting to reuse a blocked connection

Open

#526 opened on Dec 8, 2016

View on GitHub
 (10 comments) (5 reactions) (0 assignees)Go (9,946 stars) (1,789 forks)batch import
help wanted

Description

Issue description

the latest version: 1.3.

Prepare one statement and execute it on one transaction, keep rows open. Error happens when trying to prepare another statement: [mysql] 2016/12/08 15:45:57 packets.go:431: busy buffer

I see issue#314 which was similiar with the problem and closed. Looks like this problem not fixed in 1.3.

Example code

func query(db *sql.DB) {
	var (
		tx    *sql.Tx
		stmt1 *sql.Stmt
		stmt2 *sql.Stmt
		rs1   *sql.Rows
		rs2   *sql.Rows
	)

	tx, _ = db.Begin()
	stmt1, _ = tx.Prepare("select f1, f2 from test where f2 = 11")
	rs1, _ = stmt1.Query()
	rs1.Next()

	stmt2, _ = tx.Prepare("select f2 from test where f2 = 111")  // error here
	rs2, _ = stmt2.Query()
	rs2.Next()

}

Error log

[mysql] 2016/12/08 15:45:57 packets.go:431: busy buffer

Configuration

*Driver version:1.3

Go version: go version go1.7.1 windows/amd64,go version go1.7.4 linux/amd64

Contributor guide

Tech stack
go
Domain
backenddatabase
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go programmingdatabase/sql packageMySQL driver internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
The bug is about a busy buffer error when calling Prepare on a transaction that already has active rows. The error source is packets.go:431. To fix, the driver should detect that the connection buffer is busy and return a descriptive error like 'connection is busy with another result set'. Look at how conn.go manages the buffer state and ensure it is reset properly after rows are closed. Also review issue #314 for prior discussion.