Commits on Jan 29, 2024

1. Add plan-time chunk exclusion for real-time CAggs …

   The watermark function for CAggs is declared as STABLE since the value
   of the function changes after every CAgg refresh. The function
   volatility prevents the planner from replacing the function invocation
   with a constant value and executing plan time chunk exclusion. This
   leads to high planning times on hypertables with many chunks.
   
   This PR replaces the function invocation with a constant value to allow
   plan time exclusion of chunks. We perform the replacement at plan time
   instead of changing the function volatility to IMMUTABLE, because we
   want to control the constification. Only queries that access the
   underlying hypertable in a query (i.e., no queries like SELECT
   cagg_watermark(...) without any FROM condition) are rewritten. This is
   done to make sure that the query is properly invalidated when the
   underlying table changes (e.g., the watermark is updated) and the query
   is replanned on the subsequent execution.
   
   Fixes: timescale#6105, timescale#6321
   Co-authored-by: Fabrizio de Royes Mello <fabriziomello@gmail.com>

   

   jnidzwetzki and fabriziomello committed Jan 29, 2024
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