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This system variable is deprecated (because DELAYED  inserts are not supported) and subject to removal in a future MySQL release. 

As of MySQL 8.0.26, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “System Variable Privileges” . 

• max_digest_length 

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The maximum number of bytes of memory reserved per session for computation of normalized statement digests. Once that amount of space is used during digest computation, truncation occurs: no further tokens from a parsed statement are collected or figure into its digest value. Statements that differ only after that many bytes of parsed tokens produce the same normalized statement digest and are considered identical if compared or if aggregated for digest statistics. 

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## Warning 

Setting max_digest_length  to zero disables digest production, which also disables server functionality that requires digests, such as MySQL Enterprise Firewall. 

Decreasing the max_digest_length  value reduces memory use but causes the digest value of more statements to become indistinguishable if they differ only at the end. Increasing the value permits longer statements to be distinguished but increases memory use, particularly for workloads that involve large numbers of simultaneous sessions (the server allocates max_digest_length  bytes per session). 

The parser uses this system variable as a limit on the maximum length of normalized statement digests that it computes. The Performance Schema, if it tracks statement digests, makes a copy of the digest value, using the performance_schema_max_digest_length . system variable as a limit on the maximum length of digests that it stores. Consequently, if performance_schema_max_digest_length  is less than max_digest_length , digest values stored in the Performance Schema are truncated relative to the original digest values. 

For more information about statement digesting, see Section 27.10, “Performance Schema Statement Digests and Sampling” . 

• max_error_count 

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