investigate the necessity of copying a mmap-ed chunk in ChunkDiskMapper

[machine424]

Proposal

prometheus/tsdb/chunks/head_chunks.go

Lines 767 to 771 in 594b317

	// Make a copy of the chunk data to prevent a panic occurring because the returned
	// chunk data slice references an mmap-ed file which could be closed after the
	// function returns but while the chunk is still in use.
	chkDataCopy := make([]byte, len(chkData))
	copy(chkDataCopy, chkData)

was added here #8723 to prevent a panic.

• The test no longer runs on CI: fix it and see if the panic still occurs.
• Maybe

  prometheus/tsdb/head.go

  Lines 1145 to 1148 in 594b317

  	// WaitForPendingReadersInTimeRange waits for queries overlapping with given range to finish querying.
  	// The query timeout limits the max wait time of this function implicitly.
  	// The mint is inclusive and maxt is the truncation time hence exclusive.
  	func (h *Head) WaitForPendingReadersInTimeRange(mint, maxt int64) {

  can help.

slack discussion: https://cloud-native.slack.com/archives/C01AUBA4PFE/p1709929295106999