oracle standby server not in sync with the primary server

Physical or logical standby?

Was managed recovery started?

Of course the biggest question would be is log 38 there?

Realistically, you are looking at over 130,000 archives.  It would probably be faster to recreate the standby than to apply all those logs.  I can't imagine you have the storage for that many archives.

we have a physical standby

I see this error under alert.log ( many times because I used flashback_on and flashback_of manythimes

FAL[client]: Failed to request gap sequence
GAP - thread 1 sequence 35-137288
........................
......................
ORA-16037: user requested cancel of managed recovery operation

if the logs exist:  no,  archive logs from 38-to 137110 !!!!!!!!!!!

You would have to restore all the archives that are missing and then apply them.  If you even have all those archives around somewhere.

If they don't exist on a backup somewhere, your only choice is to rebuild the standby.

Like I said originally, even if you have all the archives, rebuilding would be faster anyway.  I cannot imagine that a full restore would be slower than applying that many logs.

doing more search I found that
on the standby: I have archive logs for the day I used flash back like this:

from sq#137001(Jul 29 00:08) to sq#137108 (jul 29 19:54) exist on both primary and secondary
then at  Jul 29 19:59 (arround the time I opened the standby) archivelog started from sq#1 =>sq#37
(this doesn't exist on the primary)

then Jul 29 20:53(around the time I closed the standby) sq#137111 => sq#137123 ( which des exist on the primay) just missing sq#137109 and sq#13710

from that day, I do receive all the archive logs, but doesn't get applied

what can I do, knowing on the flash back did truncate a table that I truncated after on primary)

see result of the following query executed on the standby

select  sequence#,status,first_time, applied from v$archived_log;
 SEQUENCE# S FIRST_TIM APP
---------- - --------- ---
    137111 A 29-JUL-15 NO
    137112 A 29-JUL-15 NO
    137114 A 29-JUL-15 NO
    137115 A 29-JUL-15 NO
    137117 A 29-JUL-15 NO
........................
.........................
    137303 A 31-JUL-15 NO
    137304 A 31-JUL-15 NO

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result starts from sq#137111 to sq#137304(my last sq on both primary and standby) with APPLIED =NO for all of the returned rows

hope this helps to give me an idea on how to fix the issue!!

I'm quite confused as to what you have done as you aren't listing out the steps.  In the documentation, the only thing that I see that pertains to using flashback with a standby appears to convert the standby to the new primary.

Is it that you stopped managed recovery and need to restart it?  That should be what you would normally do with the standby when bringing it up.  The steps to do that are outlined many times in the documentation.

I am not sure, I used a script that the previous dba was using to turn on the flashback to copy some data than turn off the flash back.

how to check if my manager recovery is started or stopped.
if stopped, is it safe to just turn it on?

It should be safe to restart it.  If it isn't, the database will certainly tell you.

As it seems you have things scripted, I would suspect that there is a script to restart the database that would include restarting managed recovery.

can you please walk me through on how to :

* check if the  manager recovery is tarted or not
* if not how to start it and make it apply the archive logs starting with a specific one ( since I am copying the missing archives from the primary to the standby)

* how to check if the data are in sync beside checking if the archive logs are applied or not?

The documentation is your friend.

How to start:

http://docs.oracle.com/cd/E11882_01/server.112/e41134/log_apply.htm#SBYDB00515

You do not need to tell it where to start.  It always starts after the last log applied.

How to monitor:

http://docs.oracle.com/cd/E11882_01/server.112/e41134/manage_ps.htm#SBYDB00555

when you start the managed recovery, does it increment applying  the logs by sequence number? or by creation date?

also, is the standby needs to be on archivelog mode ?

 SELECT PROCESS, STATUS FROM V$MANAGED_STANDBY;

PROCESS   STATUS
--------- ------------
ARCH      CONNECTED
RFS       IDLE
RFS       IDLE

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select process from  v$managed_standby where process like 'MRP%';

no rows selected

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 SELECT PROCESS,STATUS,thread#,sequence#,block#,blocks
  FROM V$MANAGED_STANDBY order by thread#,process;23:36:20   2

PROCESS   STATUS          THREAD#  SEQUENCE#     BLOCK#     BLOCKS
--------- ------------ ---------- ---------- ---------- ----------
ARCH      CONNECTED             0          0          0          0
ARCH      CONNECTED             0          0          0          0
ARCH      CONNECTED             0          0          0          0
MRP0      WAIT_FOR_GAP          1         35          0          0
RFS       IDLE                  1     137864      79731        606

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is there a way to start managed recovery at a specific sequence(archived log file)??

No.  You cannot skip logs.  That would give you an inconsistent copy.  You have to apply all the logs.