Firestore: Reading Document Issue - Document Can Not Be Found

For my Android App I am using Googles' Firebase.Firestore NOSQL database in order to store some data in a cloud DB.

I has no problem to save the data, but retrieving was not working.

So I reduced my test data structure to a minimum and tried all methods described in the documentation without success.

My - not working - minimal test data structure was:

This structure represents a collection of tests ("Tsts") of my App, containing one document for each version of my App, in this case version 11.
The document 11 contains a collection ("Devs") of devices for each device on with my app has been tested.

The solution of the problem was adding a field to the document 11, for example like this:

For testing how to read the data, I used the following code based on the Firestore documentation (Sub-chapter: Get a document).

DocumentReference docRef1 = mDB.collection("Tsts").document("11");

docRef1.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {

    @Override

    public void onComplete(@NonNull Task<DocumentSnapshot> task) {

        if (task.isSuccessful()) {

            DocumentSnapshot document = task.getResult();

            if (document.exists()) {

                mLog.debug("DocumentSnapshot data: {}", document.getData());

            } else {

                mLog.debug("No document");

            }

        } else {

            mLog.debug("get failed with ", task.getException());

        }

    }

});

Only after adding the test field "field1", I could read something.
Before adding field1, I always got the message "No document" in the logs.

I hope this info helps someone.

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Flashback Database After Failover: Correcting "Error ORA-38754: FLASHBACK DATABASE not started"

If the alert log file of the former primary DB contains the following error messages:

. . .

FLASHBACK DATABASE TO SCN 6693334

ORA-38754 signalled during: FLASHBACK DATABASE TO SCN 6693334...

. . .

Try to perform a flashback manually and you might get the following error:

SQL> FLASHBACK DATABASE TO SCN 6693334;

FLASHBACK DATABASE TO SCN 6693334

*

ERROR at line 1:

ORA-38754: FLASHBACK DATABASE not started; required redo log is not available

ORA-38762: redo logs needed for SCN 6691520 to SCN 6693334

ORA-38761: redo log sequence 124 in thread 1, incarnation 13 could not be accessed

In this case . . .

. . . on the new standby DB (former primary DB - before the failover),

use rman by connecting to the local DB and using the control file (NOCATALOG):

rman target=/ NOCATALOG

or (if baseenv from Triivadis is available - with history)

rmanh target=/ NOCATALOG

Since this command using the SCN did not return any archivelogs . . .

RMAN> LIST ARCHIVELOG SCN BETWEEN 6691520 AND 6693334;

. . . I searched for the backup of the archivelog with sequence 124 by guessing the time range . . .

LIST BACKUP OF ARCHIVELOG

      FROM TIME "TO_DATE('2018.05.01 20:00:00','YYYY.MM.DD HH24:MI:SS')"

      UNTIL TIME "TO_DATE('2018.05.02 12:00:00','YYYY.MM.DD HH24:MI:SS')";

. . . and was lucky and got the SCN of the desired archivelog (SCN 6691790) (but for restoring I choose the Low SCN of the previous archivelog i.e. 6689656 )

BS Key  Size       Device Type Elapsed Time Completion Time

------- ---------- ----------- ------------ -------------------

343     60.00M     SBT_TAPE    00:00:52     2018-05-02 10:57:31

        BP Key: 343   Status: AVAILABLE  Compressed: NO  Tag: TAG20180502T105639

        Handle: 6446830_C0200Z01_c9t1sib7_1_1   Media: V_3683633_19130778

  List of Archived Logs in backup set 343

  Thrd Seq     Low SCN    Low Time            Next SCN   Next Time

  ---- ------- ---------- ------------------- ---------- ---------

. . .

  1    122     6687465    2018-05-02 10:27:49 6689656    2018-05-02 10:42:47

  1    123     6689656    2018-05-02 10:42:47 6691790    2018-05-02 10:56:38

  1    124     6691790    2018-05-02 10:56:38 6691798    2018-05-02 10:56:38

HINT

It can happen, that the needed archivelog, belongs to another incarnation of the DB.

(If this is the case - on Oracle 12c - you can use the incarnation number with the rman restore statement.)

This statement list your incarnations.

RMAN> list incarnation;

List of Database Incarnations

DB Key  Inc Key DB Name  DB ID            STATUS  Reset SCN  Reset Time

------- ------- -------- ---------------- --- ---------- ----------

1       1       DB200Z01 2998214488       PARENT  1          2018-04-20 08:00:24

2       2       DB200Z01 2998214488       PARENT  2449245    2018-04-23 07:56:18

. . .

11      11      DB200Z01 2998214488       PARENT  5928815    2018-05-01 09:13:12

12      12      DB200Z01 2998214488       PARENT  6070931    2018-05-01 13:49:26

13      13      DB200Z01 2998214488       CURRENT 6179737    2018-05-01 14:47:30

==> Incarnation 13 is current (I do not need to use it with the restore statement)

Performing the restore of the archivelog (adapt the PARMS= for your needs):

RUN {

  ALLOCATE CHANNEL ch1 TYPE 'sbt_tape' PARMS="SBT_LIBRARY=/opt/hds/Base/libobk.so";

  # ALLOCATE CHANNEL ch1 TYPE disk;

  #

  RESTORE ARCHIVELOG FROM SCN 6689656;  # INCARNATION 13;

}

Output

allocated channel: ch1

channel ch1: SID=778 device type=SBT_TAPE

channel ch1: CommVault Systems for Oracle: Version 11.0.0(BUILD80)

Starting restore at 2018-05-02 13:15:52

archived log for thread 1 with sequence 125 is already on disk as file +U02/DB200Z01_HSB1/ARCHIVELOG/2018_05_02/thread_1_seq_125.759.975063515

. . .

archived log for thread 1 with sequence 133 is already on disk as file +U02/DB200Z01_HSB1/ARCHIVELOG/2018_05_02/thread_1_seq_133.741.975064009

channel ch1: starting archived log restore to default destination

channel ch1: restoring archived log

archived log thread=1 sequence=123

channel ch1: restoring archived log

archived log thread=1 sequence=124

channel ch1: reading from backup piece 6446830_DB200Z01_c9t1sib7_1_1

Now the standby DB should by able to automatically perform a flashback.

I hope it helps.

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