How is "Allocated" field in mouse over on Agents column in Builds tab stored?

That information is maintained in-memory by the Cluster Manager, not saved to the database (for performance reasons -- you wouldn't like it much if the CM triggered a database write every. single. time. that emake requested agents!)

However, you can get the data via `cmtool getBuilds`, which includes `maxAgents`, as well as `requestedAgents`, `allocatedAgents`, and `totalAgents` for builds that are currently running. For example:

# ./cmtool --server localhost getBuilds --filter "result = -1"
<?xml version="1.0" encoding="UTF-8"?>
<responses xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="accelerator-output.xsd" version="2.0">
  <response requestId="1">
    <build>
      <buildId>385268</buildId>
      <breakPointExists>0</breakPointExists>
      <buildClassName>default</buildClassName>
      <buildName>default_385268_20190913155050</buildName>
      <duration>20453</duration>
      <hostName>chester</hostName>
      <ipAddress>172.16.3.75</ipAddress>
      <jobcacheLicenseStatus>0</jobcacheLicenseStatus>
      <maxAgents>30</maxAgents>
      <platform>linux</platform>
      <priority>120</priority>
      <result>-1</result>
      <startTime>2019-09-13T22:50:50.528Z</startTime>
      <userName>ericm</userName>
      <buildClassId>1</buildClassId>
      <requestedAgents>1</requestedAgents>
      <allocatedAgents>1</allocatedAgents>
      <totalAgents>16</totalAgents>
      <hasBuildLicense>true</hasBuildLicense>
    </build>
  </response>
</responses>

Those are the figures used for the popup you described, as well as to determine the dimensions of the bar that is rendered.