taosdata/TDengine

查询时会出现耗时很长的问题

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#34011 opened on Dec 22, 2025

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Description

sql语句：select last(ts) as ts, last(value) as val from test_260 where ts >= '2025-08-01 00:00:00' and ts <= '2025-08-31 23:59:59' INTERVAL (1d) SLIDING (1d) FILL(prev); test_260是子表，一个月内数据量大于50w条，快时几百ms就出结果，慢时会出现60s以上，查询的时候可能有服务在往时序库写数据，也观察过cpu和内存占用百分比不是很多。测试环境也模拟这样的数据量，测试不同表的查询一直无法复现超时的问题。目前不清楚怎么分析出现这种情况的具体原因，是否有其他工具或者命令分析出在查询这种sql语句时，数据交换或者其他原因的

Contributor guide

Tech stack
c
Domain
databaseperformance
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
TDengine basicsQuery profilingTime series data modeling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
To analyze this intermittent query performance issue, start by examining the query execution plan using EXPLAIN to understand the query steps. Check system logs for any warnings or errors during the slow queries. Use TDengine's performance monitoring tools like SHOW QUERIES to see if there are blocking operations. Attempt to reproduce the issue by simulating concurrent writes with similar data patterns. Investigate if the issue is related to disk I/O or cache eviction by monitoring system resources. Look for similar issues in the repository or community discussions.