Do not insert the number of healthy pieces for segment health anymore.
Rather, insert the segment health calculated by our new priority
function.
Change-Id: Ieee7fb2deee89f4d79ae85bac7f577befa2a0c7f
Query nodes table using AS OF SYSTEM TIME '-10s' (by default) when on CRDB to alleviate contention on the nodes table and minimize CRDB retries. Queries for standard uploads are already cached, and node lookups for graceful exit uploads has retry logic so it isn't necessary for the nodes returned to be current.
The chief segment health models we've come up with are the "immediate
danger" model and the "survivability" model. The former calculates the
chance of losing a segment becoming lost in the next time period (using
the CDF of the binomial distribution to estimate the chance of x nodes
failing in that period), while the latter estimates the number of
iterations for which a segment can be expected to survive (using the
mean of the negative binomial distribution). The immediate danger model
was a promising one for comparing segment health across segments with
different RS parameters, as it is more precisely what we want to
prevent, but it turns out that practically all segments in production
have infinite health, as the chance of losing segments with any
reasonable estimate of node failure rate is smaller than DBL_EPSILON,
the smallest possible difference from 1.0 representable in a float64
(about 1e-16).
Leaving aside the wisdom of worrying about the repair of segments that
have less than a 1e-16 chance of being lost, we want to be extremely
conservative and proactive in our repair efforts, and the health of the
segments we have been repairing thus far also evaluates to infinity
under the immediate danger model. Thus, we find ourselves reaching for
an alternative.
Dr. Ben saves the day: the survivability model is a reasonably close
approximation of the immediate danger model, and even better, it is
far simpler to calculate and yields manageable values for real-world
segments. The downside to it is that it requires as input an estimate
of the total number of active nodes.
This change replaces the segment health calculation to use the
survivability model, and reinstates the call to SegmentHealth() where it
was reverted. It gets estimates for the total number of active nodes by
leveraging the reliability cache.
Change-Id: Ia5d9b9031b9f6cf0fa7b9005a7011609415527dc
A few weeks ago it was discovered that the segment health function
was not working as expected with production values. As a bandaid,
we decided to insert the number of healthy pieces into the segment
health column. This should have effectively reverted our means of
prioritizing repair to the previous implementation.
However, it turns out that the bandaid was placed into the code which
removes items from the irreparable db and inserts them into the repair
queue.
This change: insert number of healthy pieces into the repair queue in the
method, RemoteSegment
Change-Id: Iabfc7984df0a928066b69e9aecb6f615253f1ad2
There is a new checker field called statsCollector. This contains
a map of stats pointers where the key is a stringified redundancy
scheme. stats contains all tagged monkit metrics. These metrics exist
under the key name, "tagged_repair_stats", which is tagged with the
name of each metric and a corresponding rs scheme.
As the metainfo observer works on a segment, it checks statsCollector
for a stats corresponding to the segment's redundancy scheme. If one
doesn't exist, it is created and chained to the monkit scope. Now we can call
Observe, Inc, etc on the fields just like before, and they have tags!
durabilityStats has also been renamed to aggregateStats.
At the end of the metainfo loop, we insert the aggregateStats totals into the
corresponding stats fields for metric reporting.
Change-Id: I8aa1918351d246a8ef818b9712ed4cb39d1ea9c6
We did not test the SegmentHealth function with actual production
values, and it turns out that values such as 52 healthy, 35 minimum
result in +Inf segment health - so pretty much all segments put into the
repair queue have the same health, which means we effectively aren't
sorting by health.
This change inserts numHealthy as segment health into the database so
the segments are ordered as they were before. We need to refine the
SegmentHealth function before we can support multi RS.
Change-Id: Ief19bbfee3594c5dfe94ca606bc930f05f85ff74
Rather than having a single repair override value, we will now support
repair override values based on a particular segment's RS scheme.
The new format for RS override values is
"k/o/n-override,k/o/n-override..."
Change-Id: Ieb422638446ef3a9357d59b2d279ee941367604d
We plan to add support for a new Reed-Solomon scheme soon, but our
repair queue orders segments by least number of healthy pieces first.
With a second RS scheme, fewer healthy pieces will not necessarily
correlate to lower health.
This change just adds the new column in a migration. A separate change
will add the new health function.
Right now, since we only support one RS scheme, behavior will not
change. Number of healthy pieces is being inserted as "segment health"
until the new health function is merged.
Segment health is calculated with a new priority function created in
commit 3e5640359. In order to use the function, a new config value is
added, called NodeFailureRate, representing the approximate probability
of any individual node going down in the duration of one checker run.
Change-Id: I51c4202203faf52528d923befbe886dbf86d02f2
The current monkit reporting for "remote_segments_lost" is not usable for
triggering alerts, as it has reported no data. To allow alerting, two new
metrics "checker_segments_below_min_req" and "repairer_segments_below_min_req"
will increment by zero on each segment unless it is below the minimum
required piece count. The two metrics report what is found by the checker
and the repairer respectively.
Change-Id: I98a68bb189eaf68a833d25cf5db9e68df535b9d7
A change was made to use a metabase.SegmentKey (a byte slice alias)
as the last seen item to iterate through the irreparable DB in a
for loop. However, this SegmentKey was not initialized, thus it was
nil. This caused the DB query to return nothing, and healthy segments
could not be cleaned out of the irreparable DB.
Change-Id: Idb30d6fef6113a30a27158d548f62c7443e65a81
As part of the Metainfo Refactoring, we need to make the Metainfo Loop
working with both the current PointerDB and the new Metabase. Thus, the
Metainfo Loop should pass to the Observer interface more specific Object
and Segment types instead of pb.Pointer.
After this change, there are still a couple of use cases that require
access to the pb.Pointer (hence we have it as a field in the
metainfo.Segment type):
1. Expired Deletion Service
2. Repair Service
It would require additional refactoring in these two services before we
are able to clean this.
Change-Id: Ib3eb6b7507ed89d5ba745ffbb6b37524ef10ed9f
Repair workers prioritize the most unhealthy segments. This has the consequence that when we
finally begin to reach the end of the queue, a good portion of the remaining segments are
healthy again as their nodes have come back online. This makes it appear that there are more
injured segments than there actually are.
solution:
Any time the checker observes an injured segment it inserts it into the repair queue or
updates it if it already exists. Therefore, we can determine which segments are no longer
injured if they were not inserted or updated by the last checker iteration. To do this we
add a new column to the injured segments table, updated_at, which is set to the current time
when a segment is inserted or updated. At the end of the checker iteration, we can delete any
items where updated_at < checker start.
Change-Id: I76a98487a4a845fab2fbc677638a732a95057a94
Another change which is a part of refactoring to replace path parameter
(string/[]byte) with key paramter (metabase.SegmentKey)
Change-Id: I617878442442e5d59bbe5c995f913c3c93c16928
* add monkit stat new_remote_segments_needing_repair, which reports the
number of new unhealthy segments in the repair queue since the previous
checker iteration
Change-Id: I2f10266006fdd6406ece50f4759b91382059dcc3
* Delete expired segments in expired segments service using metainfo
loop
* Add test to verify expired segments service deletes expired segments
* Ignore expired segments in checker observer
* Modify checker tests to verify that expired segments are ignored
* Ignore expired segments in segment repairer and drop from repair queue
* Add repair test to verify that a segment that expires after being
added to the repair queue is ignored and dropped from the repair queue
Change-Id: Ib2b0934db525fef58325583d2a7ca859b88ea60d
In production, the satellite is overriding the default repair threshold
(35) to a higher value (52). In some places in the checker and
irreparable processes, the repair threshold on the redundancy scheme is
used in place of the override value. This fixes those cases.
Change-Id: Ie7387217d9fb3886f050b5e5b67be51f276196de
Add a column to the repair queue table in the satellite db for healthy
piece count. When an item is selected from the repair queue, the least
durable segment that has not been attempted in the past hour should be
selected first. This prevents our repairer from getting stuck doing work
on segments that are close to the repair threshold while allowing
segments that are more unhealthy to degrade further.
The migration also clears the repair queue so that the migration runs
quickly and we can properly account for segment health in future repair
work.
We do not select items off the repair queue that have been attempted in
the past six hours. This was changed from on hour to allow us time to
try a wider variety of segments when the repair queue is very large.
Change-Id: Iaf183f1e5fd45cd792a52e3563a3e43a2b9f410b
this commit updates our monkit dependency to the v3 version where
it outputs in an influx style. this makes discovery much easier
as many tools are built to look at it this way.
graphite and rothko will suffer some due to no longer being a tree
based on dots. hopefully time will exist to update rothko to
index based on the new metric format.
it adds an influx output for the statreceiver so that we can
write to influxdb v1 or v2 directly.
Change-Id: Iae9f9494a6d29cfbd1f932a5e71a891b490415ff
