alibaba/druid · error · IllegalArgumentException

illegal initialSize {}, maxActive {}

Error message

illegal initialSize {}, maxActive {}

What it means

IllegalArgumentException thrown during init() when getInitialSize() > maxActive. initialSize controls how many connections are created eagerly at startup; creating more than the pool's maximum would immediately overflow the pool, so Druid rejects the combination.

Source

Thrown at core/src/main/java/com/alibaba/druid/pool/DruidDataSource.java:727

                    cacheServerConfigurationSet = true;
                } else if (this.jdbcUrl.indexOf("cacheServerConfiguration") != -1) {
                    cacheServerConfigurationSet = true;
                }
                if (cacheServerConfigurationSet) {
                    this.connectProperties.put("cacheServerConfiguration", "true");
                }
            }

            if (maxActive <= 0) {
                throw new IllegalArgumentException("illegal maxActive " + maxActive);
            }

            if (maxActive < minIdle) {
                throw new IllegalArgumentException("illegal maxActive " + maxActive);
            }

            if (getInitialSize() > maxActive) {
                throw new IllegalArgumentException("illegal initialSize " + this.initialSize + ", maxActive " + maxActive);
            }

            if (timeBetweenLogStatsMillis > 0 && useGlobalDataSourceStat) {
                throw new IllegalArgumentException("timeBetweenLogStatsMillis not support useGlobalDataSourceStat=true");
            }

            if (maxEvictableIdleTimeMillis < minEvictableIdleTimeMillis) {
                throw new SQLException("maxEvictableIdleTimeMillis must be grater than minEvictableIdleTimeMillis");
            }

            if (keepAlive && keepAliveBetweenTimeMillis <= timeBetweenEvictionRunsMillis) {
                throw new SQLException("keepAliveBetweenTimeMillis must be greater than timeBetweenEvictionRunsMillis");
            }

            if (this.driverClass != null) {
                this.driverClass = driverClass.trim();
            }

View on GitHub (pinned to fa8dc99126)

Solutions

1. Set initialSize <= maxActive.
2. For warm-up, scale both initialSize and maxActive up together (e.g. initialSize=5, maxActive=20).
3. Leave initialSize at default (or 0) if you do not need eager warm-up.

Example fix

# before
druid.initialSize=10
druid.maxActive=5
# after
druid.initialSize=5
druid.maxActive=20

if (dataSource.getInitialSize() > dataSource.getMaxActive()) {
    throw new IllegalStateException("initialSize (" + dataSource.getInitialSize()
        + ") must be <= maxActive (" + dataSource.getMaxActive() + ")");
}

When it happens

Trigger: init() runs with this.initialSize > maxActive. The check at line 726 throws, reporting both values.

Common situations: initialSize set high for fast warm-up while maxActive left small; default initialSize larger than an intentionally tiny maxActive; config drift between environments.

Related errors

• illegal maxActive {}
• maxActive less than minIdle, {} < {}
• maxActive can't not set zero
• timeBetweenLogStatsMillis not support useGlobalDataSourceSta
• maxEvictableIdleTimeMillis must be grater than minEvictableI

AI-assisted analysis of alibaba/druid@fa8dc99126 (2026-08-14). Data as JSON: /api/errors/75163dd739e5ad9c. Report an issue: GitHub.