release-21.1: sql: only create real spans when session tracing/sampling #61965
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This is a "by-hand" revert of 842d79b and motivates the next commit. The only "by-hand" bits comes from wanting to retain the comments added in that commit. To reduce the memory overhead for tracing, statements will stop using real spans unless absolutely required (for e.g. when SET TRACING = on). The intent behind cockroachdb#61532 was to reduce the overhead of sampled statements by not creating an additional new span when one was already available (the statement's span). Well, with the next commit, the statement's span will be a no-op one, so when we know that we're sampling we'll want create a new span. In the end, with respect to spans created, we'll be doing no worse for sampled statements relative to cockroachdb#61532. Release note: None
This drastically reduces the memory overhead for tracing we're observing in cockroachdb#59424. This commit does a few disparate things to make it happen: 1. We now access the tracing span through txnState.Ctx exclusively. This gives us a single point to hijack, which we'll later do. By default txn's are initialized with a no-op span. If later on session tracing is enabled, we'll create a real (verbose) span and swap it out with the txn's no-op one. This gives us the same semantics as earlier, and on the plus side, we're not re-using the same tracing span when session tracing is toggled. 2. Hard tracing methods to work with no-op spans. Specifically GetRecording and TraceID. 3. Remove a crash vector through crdb_internal.trace_id. It was previously reaching into the first recording to retrieve a trace ID. But it's not guaranteed that recordings are non-empty. This could be used to induce panics in the server. This PR will need to get backported to 21.1. Fixes cockroachdb#59424. Release note: None
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Backport 2/2 commits from #61777. Fixes #61710. Fixes #61696. Fixes #61718.
/cc @cockroachdb/release
This drastically reduces the memory overhead for tracing we're observing
in #59424. This commit does a few disparate things to make it happen:
gives us a single point to hijack, which we'll later do. By default
txn's are initialized with a no-op span. If later on session tracing is
enabled, we'll create a real (verbose) span and swap it out with the
txn's no-op one. This gives us the same semantics as earlier, and on the
plus side, we're not re-using the same tracing span when session tracing
is toggled.
GetRecording and TraceID.
previously reaching into the first recording to retrieve a trace ID. But
it's not guaranteed that recordings are non-empty. This could be used to
induce panics in the server.
This PR will need to get backported to 21.1. Fixes #59424.
Release note: None
+cc @cockroachdb/kv-east.