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ezpublish:
    stash_cache:
        igbinary: true/false
        lzf: true/false

• `ezpublishezpublish.stash_cache.igbinary` igbinary enables you to use the igbinary PHP extension to serialize objects stored in cache.
  • Recommended enabled in most use cases.
• `ezpublishezpublish.stash_cache.lzf` lzf enables you to use the LZF PHP extension to compress serialized objects stored in cache.
  • Compression consumes some more CPU, . A scenario where it improves overall performance is when limited by redis Redis memory and/or network bandwidth is limited, with spare CPU capacity on PHP server. 

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These options in combination results in around 1/2 memory usage for API caching compared to not being enabled, igbinary accounts for ~75% of that and LZF the remaining ~25% when configured for max compression.

After changing these settings you need to clear cache and purge Redis content .