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19a6545815
When enabling wal_compression, there is a risk to leak data similarly to the BREACH and CRIME attacks on SSL where the compression ratio of a full page image gives a hint of what is the existing data of this page. This vulnerability is quite cumbersome to exploit in practice, but doable. So this patch makes wal_compression PGC_SUSET in order to prevent non-superusers from enabling it and exploiting the vulnerability while DBA thinks the risk very seriously and disables it in postgresql.conf. Back-patch to 9.5 where wal_compression was introduced.