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Wal difference in PostgreSQL


Here is the function can calculate the no.of files difference between the two wail files, and will give you an exact results.

CREATE OR REPLACE FUNCTION public.hot_standby_lag(primary_xlog_loc text, slave_xlog_replay_loc text)
 RETURNS integer
 LANGUAGE plpgsql
AS $function$
Digit_Length int;
Query text;
No_of_Bits int;
No_of_Walfiles int;
No_of_Zeros int:=0;
Cnt int:=0;
Re_Formatted_Primary_Log text;
Re_Formatted_Slave_Log text;
_1 int;
_2 int;
_3 int;
select GREATEST(length(trim(substring($1 for 8),'0')||trim(substring($1 from 9 for 8),'0')||ltrim(substring($1 from 17 for 8),'0')),length(ltrim(substring($2 for 8),'0')||trim(substring($2 from 9 for 8),'0')||ltrim(substring($2 from 17 for 8),'0'))) into Digit_Length;

select GREATEST(length(ltrim(substring($1 for 8),'0')),length(ltrim(substring($2 for 8),'0'))) into _1;
select GREATEST(length(trim(substring($1 from 9 for 8),'0')),length(trim(substring($2 from 9 for 8),'0'))) into _2;
select GREATEST(length(ltrim(substring($1 from 17 for 8),'0')),length(ltrim(substring($2 from 17 for 8),'0'))) into _3;

if _3 != 2 then
raise notice 'enterted';
end if;
raise notice '%',Digit_Length;

select ('x'||lpad(ltrim(substring(PRIMARY_XLOG_LOC for 8),'0'),_1,'0')||lpad(trim(substring(PRIMARY_XLOG_LOC from 9 for 8),'0'),_2,'0')||lpad(ltrim(substring(PRIMARY_XLOG_LOC from 17 for 8),'0'),2,'0')) into Re_Formatted_Primary_Log;
Raise notice '%',Re_Formatted_Primary_Log;

select ('x'||lpad(ltrim(substring(SLAVE_XLOG_REPLAY_LOC for 8),'0'),_1,'0')||lpad(trim(substring(SLAVE_XLOG_REPLAY_LOC from 9 for 8),'0'),_2,'0')||lpad(ltrim(substring(SLAVE_XLOG_REPLAY_LOC from 17 for 8),'0'),2,'0')) into Re_Formatted_Slave_Log;
raise notice '%',Re_Formatted_Slave_Log;

select GREATEST(length(regexp_replace(Re_Formatted_Primary_Log::text,'[^0]','','g')),length(regexp_replace(Re_Formatted_Slave_Log::text,'[^0]','','g'))) into Cnt;

Query:='select (select '''||Re_Formatted_Primary_Log||'''::bit('||No_Of_Bits||')::bigint) - (select '''||Re_Formatted_Slave_Log||'''::bit('||No_Of_Bits||')::bigint)';
raise notice '%',Query;
execute query into No_of_Walfiles;
return No_of_Walfiles;

Here, i tweaked the logic behind the hex decimal file names and will give you the exact resutls.

Hope this helps in warm standby/hot standby no.of files delay..



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