Is there a way to ask PostgreSQL which queries it has the most trouble with?

Question

PostgreSQL

There is a mobile application, it has a backend with PostgreSQL 9.5. Performance issues have recently become noticeable. I want to quickly find the most problematic places and perform point optimizations.
top output:

top - 18:35:10 up  1:16,  1 user,  load average: 8.77, 7.92, 7.53
Tasks: 121 total,  11 running, 110 sleeping,   0 stopped,   0 zombie
%Cpu(s): 98.3 us,  1.5 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.2 si,  0.0 st
KiB Mem :  1015752 total,    85512 free,   558960 used,   371280 buff/cache
KiB Swap:        0 total,        0 free,        0 used.   222584 avail Mem 

PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                                             
2927 postgres  20   0  310480  80120  67948 R  19.9  7.9   1:18.87 postgres                                                                                                                            
2935 postgres  20   0  310464  79044  66924 R  19.9  7.8   0:57.41 postgres                                                                                                                            
2945 postgres  20   0  310760  77708  65424 R  19.9  7.7   0:45.32 postgres                                                                                                                            
2930 postgres  20   0  310592  79872  67476 R  19.6  7.9   1:10.93 postgres                                                                                                                            
2931 postgres  20   0  310736  80796  68288 R  19.6  8.0   1:04.56 postgres                                                                                                                            
2932 postgres  20   0  310600  79392  67112 R  19.6  7.8   0:59.41 postgres                                                                                                                            
2943 postgres  20   0  310048  77436  65952 R  19.6  7.6   0:51.44 postgres                                                                                                                            
2944 postgres  20   0  310472  79192  66936 R  19.6  7.8   0:47.25 postgres                                                                                                                            
2947 postgres  20   0  310512  77936  66032 R  19.6  7.7   0:41.64 postgres                                                                                                                            
2940 postgres  20   0  310408  78816  67040 R  19.3  7.8   0:55.47 postgres

Played with shared_buffers and work_mem, but did not notice any changes.
Now shared_buffers = 128mb, work_mem = 24mb.

Answer 1

You can enable logging of slow queries , and then run these queries with EXPLAIN ANALYZE and see the execution plan.