Introduction

This document aims to summarise the outcome of the recent performance testing conducted by the PTF team and provide some suggestions as to how we might improve the performance of checking out an item under load.

Context

History

Development of modules within the circulation domain started early in FOLIO's overall development, meaning they are some of the oldest modules and integrate heavily with other older modules.

Historical Constraints

When FOLIO started, it began with some constraints that were applied when these modules were developed.

I've picked out a few that could be relevant to how we got to the current design

• Business logic must the most current state for decisions
• Business logic and storage are split in two separate modules (in order to support independent substitution)
• All integration between modules is done via HTTP APIs (proxied via Okapi)
• All data is stored within PostgreSQL
• A record oriented design with a single system of record for each record type (business logic / storage separation not-withstanding)

Some of these have changed since this early development e.g. the use of Kafka for integration.

Some may need to change for the options below to be tolerable and coherent within FOLIO.

Expectations

A checkout (including the staff member scanning the item barcode) must complete within 1 second (from the documented /wiki/spaces/DQA/pages/2658550). It is stated that this includes the time for a person to scan the item barcode.

For the purposes of this analysis I shall assume the following (neither of which are likely true in practice):

• None of this time is taken up by the human scanning the barcode (and interacting with the UI)
• None of this time is taken up the FOLIO UI (in practice, the UI has to fetch item information to potentially ask the staff member some questions)

The performance requirements do not provide any guidance on what the conditions (load parameters or resource configuration) this expectation should hold for.

Thus for the purposes of this analysis, the expectation is that:

the check out API must respond within 1 second under load from 8 concurrent requests (with no tolerance for outliers that exceed this limit)

Solution Constraints

Beyond the general constraints on architectural decisions.

• No changes to the client interface of the circulation APIs
• Only existing infrastructure can be used (I'm including Kafka in this, even though it isn't official yet)

Analysis

Limitations of Analysis

Whilst we have overall performance data for (an approximation of) the whole check out process, we only have a single detailed sample of the downstream requests from the check out API. That sample is not representative of the range of response times likely present in a whole performance test run.

Thus, this analysis has to assume that the sample is representative whilst also interpreting it skeptically.

We also do not know:

• why the response times of the constituent parts do not equate to the overall response time
• what amount of time Okapi takes to process requests / responses
• what amount of time mod-circulation takes to use this information to make decisions e.g. to apply the circulation rules

This factors mean it is challenging to draw reliable and specific conclusions about the requests involved, meaning that most of the analysis will be broad and general.

What takes up the time?

There are 27 downstream requests triggered by mod-circulation during the sample check out.

Once we deduct the initial overhead (133ms) that leaves us with an approximate budget of 32ms per request (867 ms / 27).

At the moment, the average request takes 62ms (including proxying overhead). This is more than double the budget we have available.

Whilst there are some outliers that push up this number, I think this indicates the degree of challenge we have with the current approach.

What could we do?

Broadly speaking there are three things that can be done to improve the response time of a check out API request

• Reduce the amount of time each request takes
• Make downstream requests concurrently
• Reduce the quantity of downstream requests made

These ideas will be the framing for the proposal part of this document.

Options

Improve the performance of individual downstream requests

Characteristics

• Scope for improvement is limited as many of these requests are individually relatively fast
• Improvements are brittle and can be easily undone by changes to downstream modules (and it may take a while to become aware of degradation)
• Limited by the constraints of the downstream modules (e.g. the data is currently stored as JSONB)
• May involve changes in multiple modules
• Retains the same amount of downstream requests
• Retains the same overhead from Okapi proxying

Make downstream requests concurrently

For example, once the item is received, the locations, loan types and material types can be fetched concurrently.

Characteristics

• Only involves changes to mod-circulation
• Increases the complexity of the code in mod-circulation
• Not all requests can be made concurrently (some are based upon prior requests or decisions that cannot be made up front)
• Is likely limited by how well other modules / database can handle concurrent requests
• Retains the same overall load on the system as before (although it may be compressed in time)
• Retains the same amount of downstream requests
• Retains the same overhead from Okapi proxying

Combine downstream requests for related records into a single request

Introduces context-specific APIs that are intended for specific use. At most, this can only be applied to the requests made to the same module.

It may not make sense to combine all of the record types from a single module. For example, does it make sense to have an API that fetches existing open loans and loan policies together?

We are already introducing a new API in mod-inventory-storage in this manner to improve the pre-checks made by the check out UI.

Characteristics

• Reduces the amount of individual downstream requests (and hence the Okapi proxying overhead)
• Requires at least one downstream request per destination module
• Requires at least one database query per downstream module
• Might reduce the response time off the downstream request (compared to the combination of )
• Might reduce the load on downstream modules (depending upon how the combined request is handled, it is possible the load increases)
• Reduction in downstream requests is limited to number of record types within a single module
• Increases the amount of APIs to maintain (what I call the surface area of the module)
• Increases the coupling between modules (by introducing the clients context into the other module)
• Increases the coupling between the record types involved (e.g. it's harder to move record types to other modules when they are included in APIs together, changes to them ripple across APIs)

Copy data into circulation

Consume messages produced (via Kafka) by other modules to build views of the data needed to perform a check out.

The biggest challenge with this option is the community's tolerance to using potentially stale data for making decisions.

This suggests processing the messages and using a database from mod-circulation rather than mod-circulation-storage to avoid the overhead of needing to request the copied data from a downstream module.

Characteristics

• Requires no downstream requests for fetching data during check out process
• Increases the potential for stale data to be used for decisions
• Is contrary to constraints that may still be present in FOLIO
• Introduces complexity of processing messages and persistent storage into mod-circulation
• Introduces a dependency on a database from mod-circulation
• Introduces a dependency on messages produced by other modules
• State changes still require a downstream request (and the requisite proxying overhead)

Variations

Store the copied data in mod-circulation-storage

Rather than introducing a database in mod-circulation, use the database that is already used by mod-circulation-storage.

Downstream requests will be needed from mod-circulation to mod-circulation-storage to access the views.

Cache the copied data in each instance of mod-circulation

Rather than introducing a database in mod-circulation, use a volatile cache within each instance of mod-circulation and use downstream requests to populate the cache.

Downstream requests are still needed from mod-circulation to populate the cache. Response times may be less stable when the cache needs to be repopulated.

Combine the business logic and storage modules together

Characteristics

• Removes all downstream for record types within the circulation domain e.g. loans, requests, loan policies etc (include state changes e.g. creating a loan, fulfilling a request)
• Removes the distinction between business logic and storage representations of those records types
• Allows for state changes within the circulation domain to be done within a database transaction
• Is contrary to constraints that may still be present in FOLIO
• Storage modules have been used to workaround cyclic dependencies constraints in Okapi, removing them might involve changing other modules to avoid this in other ways

Appendices

Definitions

Requests made during a typical check out

The first 4 lines of the table describe the initial requests made by Okapi in reaction to the incoming request (to check out). I believe there are circumstances where these requests are made again, however that is omitted from this analysis.

Intent	Endpoint	Destination Module	Sample Response Time (ms)	Sample Response Time of Token Check (ms)
Initial request				99
Fetch user (making the request)	GET /users/{id}	mod-users	6
Fetch permissions	GET /perms/users?query=userId=={id}	mod-permissions	16
Generate downstream token			12
Fetch user (patron) by barcode	GET /users?query=barcode=={barcode}	mod-users	13	86
Fetch manual blocks	GET /manualblocks?query=userId=={userId}	mod-feesfines	133	7
Fetch automated blocks	GET /automated-patron-blocks/{userId}	mod-patron-blocks	546*	27
Fetch item by barcode	GET /item-storage/items?query=barcode=={barcode}	mod-inventory-storage	163	10
Fetch holdings	GET /holdings-storage/holdings/{id}	mod-inventory-storage	57	9
Fetch instance	GET /instance-storage/instances/{id}	mod-inventory-storage	22	7
Fetch location	GET /locations/{id}	mod-inventory-storage	9	13
Fetch library	GET /location/units/libraries/{id}	mod-inventory-storage	10	7
Fetch campus	GET /location/units/campuses/{id}	mod-inventory-storage	10	7
Fetch institution	GET /location/units/institutions/{id}	mod-inventory-storage	11	7
Fetch service point	GET /service-points/{id}	mod-inventory-storage	9	8
Fetch material type	GET /material-types/{id}	mod-inventory-storage	8	7
Fetch loan type	GET /loan-types/{id}	mod-inventory-storage	22	8
Fetch existing loans	GET /loan-storage/loans?query=status.name=="Open" and itemId=={itemId}	mod-circulation-storage	9	17
Fetch requests	GET /request-storage/requests?query=itemId=={itemId} and status==("Open - Not yet filled" or "Open - Awaiting pickup" or "Open - In transit" or "Open - Awaiting delivery") sortBy position/sort.ascending	mod-circulation-storage	10	9
Fetch circulation rules	GET /circulation/rules	mod-circulation-storage	18	18
Fetch loan policy	GET /loan-policy-storage/loan-policies/{id}	mod-circulation-storage	10	8
Fetch tenant locale	GET /configurations/entries?query=module=="ORG" and configName=="localeSettings"	mod-configuration	16	10
Fetch overdue fines policies	GET /overdue-fines-policies/{id}	mod-feesfines	19	8
Fetch lost item fees policies	GET /lost-item-fees-policies/{id}	mod-feesfines	11	10
Fetch opening days	GET /calendar/periods/7068e104-aa14-4f30-a8bf-71f71cc15e07/calculateopening?requestedDate={{dueDate}}	mod-calendar	12	8
Fetch user (patron) groups	GET /groups?query=id=={groupId}	mod-users	17	7
Update item status	PUT /item-storage/items/{id}	mod-inventory-storage	194	13
Create loan	POST /loan-storage/loan	mod-circulation-storage	16	8
Update patron action session	POST /patron-action-session-storage/patron-action-sessions	mod-circulation-storage	10	7
Fetch user	GET /users/{id}	mod-users	6	15
Fetch patron notice policy	GET /patron-notice-policy-storage/patron-notice-policies/1a821238-0cd9-48d9-a71a-057d33df0154	mod-circulation-storage	6	7

* The Vega team have already done some work to improve this