feat: instrument Spanner client with OpenCensus metrics #54

mayurkale22 · 2020-01-31T19:22:05Z

Updates #53

First set of Session Pool related metrics:

cloud.google.com/java/spanner/max_allowed_sessions
The maximum number of sessions allowed. Configurable by the user. This metric is labeled by database name, instance id and library version.
cloud.google.com/java/spanner/in_use_sessions
The number of sessions currently in use (or checked out from the pool at this very moment). This metric is labeled by database name, instance id and library version.
cloud.google.com/java/spanner/max_in_use_session
The maximum number of sessions in use during the last maintenance window interval. A maintenance window is a set 10 minute interval. After a complete maintenance window has passed, the value is reset to zero (and then start increasing again). This metric is labeled by database name, instance id and library version.

I will open follow-up PRs to address other metrics mentioned in the issue.

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionPool.java

rghetia

Overall looks good.

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionPool.java

...-spanner/src/main/java/com/google/cloud/spanner/v1/stub/metrics/MetricRegistryConstants.java

skuruppu

Overall I think this looks good as well. Adding @olavloite to get his thoughts on the implementation as well since he's the most familiar with the Java client library.

olavloite

This looks generally good to me, but I would recommend changing the description of the measurement of maxSessionsInUse. I think it would confuse many users if they see a value that is only increasing (or at least never decreasing) during a period of 10 minutes that is called 'The number of active sessions'.

olavloite · 2020-02-04T17:27:28Z

...-spanner/src/main/java/com/google/cloud/spanner/v1/stub/metrics/MetricRegistryConstants.java

+  // The Metric name and description
+  public static final String ACTIVE_SESSIONS = "cloud.google.com/java/spanner/active_sessions";
+  public static final String MAX_SESSIONS = "cloud.google.com/java/spanner/max_sessions";
+  public static final String ACTIVE_SESSIONS_DESCRIPTION = "The number of active sessions";


I think the description of this metric should be different, considering it is reading maxSessionsInUse. This value will only increase during a 10 minute interval, and then be reset to zero (and then start increasing again). Suggestion, something like:
'Max number of sessions in use during the last 10 minutes'.

I noticed the other discussion about whether to measure numSessionsInUse or maxSessionsInUse. I think both could be valuable for the user, and numSessionsInUse should have a description like 'The number of sessions currently in use'.

Sure, will change the description for maxSessionsInUse. Could you please elaborate more on numSessionsInUse metric. How is it different from maxSessionsInUse and how do you think it is useful for users in conjunction with maxSessionsInUse?

Just so you know, we don't want to add too many metrics due to costs associated with exporting to backend (like stackdriver). Having said that, I am more than happy to include metrics which are meaningful (and useful) for the users to resolve/understand the production issues at some extend.

numSessionsInUse reflects the number of sessions checked out from the pool at this very moment. Depending on probe intervals and average transaction duration, this number might often be measured to be zero for a system under low load. E.g. if the system executes 1 transaction per second, the average transaction duration is 300ms and the value is probed once every 10 seconds, the chances are big that you will often measure the value between two transactions and get a zero. On a system with higher load, measuring this value will give the user a better idea about how the distribution of the transactions are over time. If this value is relatively constant most of the time, but suddenly shows a spike that cannot be correlated with a similar sudden spike in user requests, it might be an indication of a concurrency problem somewhere (locks in the database, concurrency issues in the application itself etc.).

maxSessionsInUse reflects the maximum number of numSessionsInUse during the current maintenance window. A maintenance window is a hard-coded 10 minute interval. After a complete maintenance window has passed, the value is reset to 0. The value is updated every time a session is checked out of the pool by the simple calculation maxSessionsInUse = Math.max(numSessionsInUse, maxSessionsInUse).

As you can conclude from the above (and which I also just now realized ;-)), the maxSessionsInUse has a slight flaw: If no new session is checked out during a maintenance window, the value will remain zero during the entire window, even if there are sessions that are kept checked out during the entire window (i.e. the sessions were checked out during a previous maintenance window).

Thanks for the explanation. I have added numSessionsInUse metric PTAL.

I would like to get this PR merged before adding other metrics.

olavloite

I really think you should change the packages of the MetricsRegistryConstants and MetricsRegistryTestUtils. Unless there's a very good reason for it, I would suggest placing these in the normal com.google.cloud.spanner package. Sorry for not noticing this before :-(

For the rest; LGTM

...-spanner/src/main/java/com/google/cloud/spanner/v1/stub/metrics/MetricRegistryConstants.java

google-cloud-spanner/src/test/java/com/google/cloud/spanner/v1/MetricRegistryTestUtils.java

mayurkale22 · 2020-02-05T19:32:43Z

@rghetia and @skuruppu I have addressed all the comments, PTAL. As mentioned earlier, I will work on follow-up PR to add other metrics.

rghetia · 2020-02-05T20:37:55Z

google-cloud-spanner/src/main/java/com/google/cloud/spanner/MetricRegistryConstants.java

+      "Max number of sessions in use during the last 10 minutes";
+  public static final String MAX_SESSIONS_DESCRIPTION = "The number of max sessions configured";
+  public static final String SESSIONS_IN_USE_DESCRIPTION =
+      "The number of sessions checked out from the pool";


names are confusing. I would suggest

old new Description

active_sessions max_in_use_session The max number of sessions concurrently in use during the current 10 minutes interval

max sessions max_allowed_sessions The Maximum number of sessions allowed. Configurable by the user.

sessions_in_use in_use_sessions The number of sessions currently in use

Alternatively, in_use can be replaced with 'active' in name and description.
checked out has different meaning than active/in_use. If that is appropriate, then it should be used in the name and the description.

Done in e6938bc, decided to use in_use. PTAL

skuruppu

Minor nits and a comment about the test but LGTM otherwise.

google-cloud-spanner/src/main/java/com/google/cloud/spanner/MetricRegistryConstants.java

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionPool.java

google-cloud-spanner/src/test/java/com/google/cloud/spanner/SessionPoolTest.java

Add active_sessions (The number of active sessions in use) and max_sessions (The number of max sessions configured the user) metrics

Use maxSessionsInUse instead of numSessionsInUse and update the description.

This change addes five metrics for session management: * in_use_sessions: the current number of sessions that are checked out from the session pool. * max_in_use_sessions: the maximum number of in_use_sessions in last 10 minutes. This is based on tumbling windows, instead of sliding windows. * max_allowed_sessions: the maximum number of sessions that is configured by the user. * get_sessions_timeout: the cumulative number of get sessions timeouts when pool exhaustion happens. * num_acquired_sessions: the cumulative number of sessions that are checked out from the session pool. * num_released_sessions: the cumulative number of sessions that are released back to the session pool. All metrics are tagged by: * client_id: each database has its own increasing ID sequence. For two different databases, their client IDs all start from "client-1". * database: the database ID. * instance_id: the instance ID. * library_version: the library version from google-cloud-go/internal/version which is a date in YYYYMMDD format. Notes: There are three ways to check out a session from the pool: 1) take(): get a read session called by a user 2) takeWriteSession(): get a read/write session by a user 3) getNextForTx() in healthchecker's worker (session.go:1336): healthchecker's workers convert read sessions to r/w sessions. E.g., when initializing the pool, workers check out 20 read sessions from the pool, turn them into r/w sessions, and put them back to the pool , assume that MinOpended=100 and WriteSessions=0.2. So some metrics are also emitted by case 3. This might confuse users if they are not aware of this behaviour. Related Java PRs: * googleapis/java-spanner#54 * googleapis/java-spanner#65 * googleapis/java-spanner#67 Change-Id: Ie163b08ef18ac2a47e1669fefab92d61fe8f2a82 Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/52953 Reviewed-by: kokoro <noreply+kokoro@google.com> Reviewed-by: Knut Olav Løite <koloite@gmail.com>

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mayurkale22 requested review from skuruppu and rghetia January 31, 2020 19:22

mayurkale22 commented Feb 1, 2020

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mayurkale22 changed the title ~~Instrument Spanner client with OpenCensus metrics~~ feat: instrument Spanner client with OpenCensus metrics Feb 4, 2020

skuruppu reviewed Feb 4, 2020

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skuruppu requested a review from olavloite February 4, 2020 10:21

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olavloite approved these changes Feb 4, 2020

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mayurkale22 requested review from skuruppu and rghetia February 5, 2020 01:14

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skuruppu approved these changes Feb 6, 2020

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mayurkale22 added 8 commits February 5, 2020 21:09

feat: add session metrics

5bf757e

Add active_sessions (The number of active sessions in use) and max_sessions (The number of max sessions configured the user) metrics

Fix code reviews

8bc6fc7

Use maxSessionsInUse instead of numSessionsInUse and update the description.

Change active sessions description

b3c56b5

add numSessionsInUse metric

893b446

Fix package structure

f2ebcdf

rename metric name and description

6ce5aa6

fix nits

67c9690

createMockSession for metrics validations

1525a7d

skuruppu approved these changes Feb 6, 2020

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mayurkale22 merged commit d9a00a8 into googleapis:master Feb 6, 2020

mayurkale22 deleted the session_metrics branch February 6, 2020 22:45

mayurkale22 mentioned this pull request Feb 7, 2020

feat: add session timeout metric #65

Merged

yoshi-automation mentioned this pull request Feb 8, 2020

docs(regen): update sample code to set total timeout, add API client header test #66

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mayurkale22 mentioned this pull request Feb 10, 2020

feat: add metrics to capture acquired and released sessions data #67

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feat: instrument Spanner client with OpenCensus metrics #54

feat: instrument Spanner client with OpenCensus metrics #54

mayurkale22 commented Jan 31, 2020 •

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old	new	Description
active_sessions	max_in_use_session	The max number of sessions concurrently in use during the current 10 minutes interval
max sessions	max_allowed_sessions	The Maximum number of sessions allowed. Configurable by the user.
sessions_in_use	in_use_sessions	The number of sessions currently in use

feat: instrument Spanner client with OpenCensus metrics #54

feat: instrument Spanner client with OpenCensus metrics #54

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