These variables can't be in shared state, as the following problem was
taking place:
1. Process1 call pgss_ExecutorCheckPerms(), acquire lock, update
relations and num_relations, release lock.
2. Process 2 call pgss_ExecutorCheckPerms(), acquire lock, update
num_relations = 0;
3. Process 1 read num_relations = 0 in pgss_update_entry, this value is
wrong as it was updated by Process 2.
Even if we acquire the lock in pgss_update_entry to read num_relations
and relations variable, Process 1 may end up acquiring the lock after
Process 2 has ovewritten the variable values, leading to Process 1
reading of wrong data.
By defining relations and num_relations to be static and global in
pg_stat_monitor.c we take advantage that each individual PostgreSQL
backend will have its own copy of this data, which allows us to remove
the locking in pgss_ExecutorCheckPerms to update these variables,
improving pg_stat_monitor overall performance.
Added a new view 'pg_stat_monitor_hook_stats' that provide execution
time statistics for all hooks installed by the module, following is a
description of the fields:
- hook: The hook function name.
- min_time: The fastest execution time recorded for the given hook.
- max_time: The slowest execution time recorded for the given hook.
- total_time: Total execution time taken by all calls to the hook.
- avg_time: Average execution time of a call to the hook.
- ncalls: Total number of calls to the hook.
- load_comparison: A percentual of time taken by an individual hook
compared to every other hook.
To enable benchmark, code must be compiled with -DBENCHMARK flag, this
will make the hook functions to be replaced by a function with the same
name plus a '_benchmark' suffix, e.g. hook_function_benchmark.
The hook_function_benchmark will call the original function and
calculate the amount of time it took to execute, than it will update
statistics for that hook.
Add application name to the key used to identify queries in the hash
table, this allows different applications to have separate entries in
pg_stat_monitor view if they issued the same query.
Andrew Pogrebnoy
Diego Fronza
Ibrar Ahmed