Similar to pg_stat_statements, pg_stat_monitor tracks wal data metrics
since PostgreSQL 13, the problem was that for PostgreSQL versions 11 and
12 we left the WalUsage variable declared in the stack unitialized,
thus leading to garbage values.
Fixed the problem by ignoring the WalUsage variable value for PG <= 12.
This commit brings following changes to this branch:
1) Port changes/additions TAP testing from main branch to this branch, under PG-292.
2) Changes to test cases due to GUCs change, under PG-331.
3) Call counts verfications, under PG-338.
4) Changes to github workflows to accomodate automation for TAP testing, under PG-343.
To check if a bucket has expired, a comparison of the time elapsed
since last bucket change was being done in get_next_wbucket() function
using the following line:
while ((current_usec - current_bucket_usec) > (PGSM_BUCKET_TIME
* 1000 * 1000))
The problem is that the expression compares a uint64 (current_usec)
with a int32 (PGSM_BUCKET_TIME), if a given user configures a value for
pgsm_bucket_time GUC (let's call it T) that could overflow int32 range
in the expression T*1000*1000 > 2**31-1, then the result would be a
negative integer cast to (uint64), resulting in a large uint64 value that
would evaluate the expression as false, thus never updating bucket
number.
When querying pg_stat_monitor view, for every entry it's verified if
the entry has not yet expired by calling IsBucketValid(bucket_number).
Using the entry's bucket number the function calculates if the time
since the bucket started, using shared global variable
pgss->bucket_start_time[bucket_id], is still valid.
Since pgss->bucket_start_time is not properly initialized in
get_next_wbucket(), the function IsBucketValid() will always
return false, thus not listing any entries in the view.
After fixing the problem with utility statements, this whole block:
do $$
declare
n integer:= 1;
begin
loop
PERFORM a,b,c,d FROM t1, t2, t3, t4
WHERE t1.a = t2.b AND t3.c = t4.d ORDER BY a;
exit when n = 1000;
n := n + 1;
end loop;
end $$;
Is only processed once, as those are nested statements, in order to
match the 1000 statements the GUC pg_stat_monitor.track must be set to
'all' and then back to the default of 'top' when done testing it.
There was a missing increment/decrement to exec_nested_level in
pgss_ProcessUtility hook, due to this, some utility statements could
end up being processed more than once, as PostgreSQL may recurse into
this hook for sub-statements or when processing a query string
containing multiple semicolon-separated statements.
Updated the Forum URL to point to the dedicated
pg_stat_monitor forum in `README.md` and
`CONTRIBUTING.md`, removed link to the Discord
channel to ensure that conversations are focused
to one location. Updated the table of contents in
the README.
Signed-off-by: Lenz Grimmer <lenz.grimmer@percona.com>
This commit adds following three sql based testcases:
1) Test unique application name set by user.
2) Histogram function is working properly as desired.
3) Error on insert is shown with proper message.
After the split into multiple pg_stat_monitor--1.0.XX.sql.in sql files,
where XX is the PostgreSQL version, it was forgotten to add the errors
view to the relevant files, this commit fixes that.
Added a link to pg_stat_monitor view reference in the Overview
Aded PG 14 to supported versions
Updated links in the Documentation section
modified: README.md
If a query exceeds pg_stat_monitor.pgsm_query_max_len, then it's
truncated before we save it into the query buffer (SaveQueryText).
When reading the query back, on pg_stat_monitor_internal, we allocate a
buffer for the query with length = pg_stat_monitor.pgsm_query_max_len,
the problem is that the read_query function adds a '\0' to the end of
the buffer when reading a query, thus if a query has been truncated, for
example, to 1024, when reading it back read_query will store the '\0' at
the position 1025, an out of array bounds position.
Then, when we call pfree to release the buffer, PostgreSQL notices the
buffer overrun and triggers an error assertion, the assertion calls our
error hook which attempts to acquire the shared pgss->lock before
pg_stat_monitor_internal has released it, leading to a deadlock.
To avoid the problem we add 1 more byte to the extra '\0' during palloc
call for query_text and parent_query_text.
Also, we release the lock before calling pfree, just in case PostgreSQL
finds a problem in pfree we won't deadlock again and get the error
reported correctly.
If a backend would change the application name during execution,
pg_stat_monitor would then fail to read the updated value, as it caches
the result in order to avoid calling the expensive functions
pgstat_fetch_stat_numbackends() and pgstat_fetch_stat_local_beentry().
A workaround was found, we can just read an exported GUC from
PostgreSQL backend itself, namely application_name, from utils/guc.h,
thus saving us from having to call those expensive functions.
Updated sql files (pg_stat_monitor_settings view).
Using right variable name and level checking on pgss_store:
key.toplevel = ((exec_nested_level + plan_nested_level) == 0);
Evgeniy Patlan
Ibrar Ahmed
Ibrar Ahmed
Lenz Grimmer
Anastasia Alexadrova
Diego Fronza
Naeem Akhter
Hamid Akhtar
Vadim Yalovets