chore: limit number of top level operations in services list

[srikanthccv]

Summary

Part of #4654

This is the schema of the top_level_operations

CREATE TABLE signoz_traces.top_level_operations
(
    `name` LowCardinality(String) CODEC(ZSTD(1)),
    `serviceName` LowCardinality(String) CODEC(ZSTD(1)),
    `time` DateTime DEFAULT now() CODEC(ZSTD(1))
)
ENGINE = ReplacingMergeTree
ORDER BY (serviceName, name)
TTL time + toIntervalMonth(1)
SETTINGS index_granularity = 8192

The table contains the most recent instance of the tuple (serviceName, name). And the time value is now(). We can use the time to discard the old operations that were created before the start time.

This change

• Discard the old operation
• Use a maximum of 1500 operations for the IN query (this should be enough?)
• Send all service ops to the client so we can show them to the user.

[github-actions]

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[ankitnayan]

why does frontend need to be aware of the TopLevelOperations? Shouldn't just this be a backend thing?

[srikanthccv]

We considered showing the users some of the selected top-level operations along with the warning text