[sql] Annotate sql::Recovery failure cases.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 8a6b285a336ab1a57df74bb51b1976e45c51131a..1b3b2ba2adbe450132f087a688f553d3a6e3e950 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -18994,6 +18994,10 @@ other types of suffix sets.
   <summary>Errors truncating database for Raze().</summary>
 </histogram>
 
+<histogram name="Sqlite.RecoveryFailures" enum="SqliteRecoveryFailureEnum">
+  <summary>Failure cases noted in recovery.cc.</summary>

[Ilya Sherman, 2013/11/25 22:52:25]

Please elaborate a bit more on what this histogram is measuring.  I'm assuming
it records an event every time that DB recovery is attempted and fails.  Is that
accurate?  If so, please document that in the summary.

[Scott Hess - ex-Googler, 2013/11/26 20:17:59]

I tried to augment it, but found that I was mostly writing filler.  It tracks
all of the failures in the class' implementation, for purposes of deciding which
(if any) are worth researching further and possibly developing additional
automated responses.  AFAICT, failures should always be due to system issues,
not issues with our code, so if the issue looks like "System is entirely fubar",
additional code can probably not solve the problem, while cases which could be
solved might not be worth the complexity if too few users hit them.

+</histogram>
+
 <histogram name="Sqlite.RecoveryHandle" enum="SqliteErrorCode">
   <summary>Error from sqlite3_backup_init() in sql::Recovery.</summary>
 </histogram>
@@ -24611,6 +24615,9 @@ other types of suffix sets.
   <int value="26" label="RECOVERY_EVENT_FAILED_AUTORECOVER_ICON_MAPPING">
     Failed v6/7 recovery on icon_mapping.
   </int>
+  <int value="27" label="RECOVERY_EVENT_FAILED_COMMIT">
+    Failed sql::Recovery::Recovered().
+  </int>
 </enum>
 
 <enum name="HttpAuthCount" type="int">
@@ -28971,6 +28978,55 @@ other types of suffix sets.
   <int value="20" label="SQLITE_IOERR_SHMLOCK">Unused</int>
 </enum>
 
+<enum name="SqliteRecoveryFailureEnum" type="int">
+  <summary>Failure cases noted in recovery.cc.</summary>
+  <int value="0" label="RECOVERY_FAILED_OPEN_TEMPORARY">
+    Failed to open temporary database to recover into.
+  </int>

[Ilya Sherman, 2013/11/25 22:52:25]

It's often useful to have the first bucket measure the success rate, so that you
can tell how common failures are overall.

[Scott Hess - ex-Googler, 2013/11/26 20:17:59]

I'll layer in success rates, because they don't detract from anything.  Mostly
I'm not really interested in success rates - I'm rather looking to see if an
absolute number of current cases can be addressed by a constant development
cost.  I suspect not, but I want to see data before closing it off.

Additionally, in case of success, the code will never be called again, while in
case of failure it will probably always be called for that user.  The success
and failure buckets are not necessarily comparable.

+  <int value="1" label="RECOVERY_FAILED_VIRTUAL_TABLE_INIT">
+    Failed to initialize recover vtable subsystem for connection.
+  </int>
+  <int value="2" label="RECOVERY_FAILED_VIRTUAL_TABLE_SYSTEM_SQLITE">
+    USE_SYSTEM_SQLITE in force, recovery virtual table not available.
+  </int>
+  <int value="3" label="RECOVERY_FAILED_WRITABLE_SCHEMA">
+    Failed to enable writable_schema.
+  </int>
+  <int value="4" label="RECOVERY_FAILED_ATTACH">
+    Failed to attach corrupt database to recovery database.
+  </int>
+  <int value="5" label="RECOVERY_FAILED_BACKUP_INIT">
+    Failed sqlite3_backup_init().  Error code in Sqlite.RecoveryHandle.
+  </int>
+  <int value="6" label="RECOVERY_FAILED_BACKUP_STEP">
+    Failed sqlite3_backup_step().  Error code in Sqlite.RecoveryStep.
+  </int>
+  <int value="7" label="RECOVERY_FAILED_AUTORECOVER_UNRECOGNIZED_TYPE">
+    Failed sqlite3_backup_step().  Error code in Sqlite.RecoveryStep.
+  </int>
+  <int value="8" label="RECOVERY_FAILED_AUTORECOVER_MISSING_TABLE">
+    AutoRecoverTable() could not find the target table.
+  </int>
+  <int value="9" label="RECOVERY_FAILED_AUTORECOVER_CREATE">
+    AutoRecoverTable() failed creating recovery vtable.
+  </int>
+  <int value="10" label="RECOVERY_FAILED_AUTORECOVER_INSERT">
+    AutoRecoverTable() failed copying data from recovery to target table.
+  </int>
+  <int value="11" label="RECOVERY_FAILED_AUTORECOVER_DROP">
+    AutoRecoverTable() failed to drop recovery table.
+  </int>
+  <int value="12" label="RECOVERY_FAILED_META_CREATE">
+    SetupMeta() failed to create meta recovery table.
+  </int>
+  <int value="13" label="RECOVERY_FAILED_META_QUERY">
+    GetMetaVersionNumber() failed querying recovery meta table.
+  </int>
+  <int value="14" label="RECOVERY_FAILED_META_NO_VERSION">
+    GetMetaVersionNumber() found no version row in meta table.
+  </int>
+</enum>
+
 <enum name="SqliteVersionDeprecation" type="int">
   <summary>Sqlite database version deprecation status</summary>
   <int value="0" label="DEPRECATION_DATABASE_NOT_EMPTY">