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create_delta_layer: improve misleading TODO comment #4488

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merged 3 commits into from
Jun 16, 2023
Merged

create_delta_layer: improve misleading TODO comment #4488

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2b8e097
create_delta_layer: improve misleading TODO comment
problame Jun 13, 2023
3e491bd
Merge remote-tracking branch 'origin/main' into problame/remove-confu…
problame Jun 15, 2023
cc419d1
address https://github.com/neondatabase/neon/pull/4488#discussion_r12…
problame Jun 15, 2023
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17 changes: 10 additions & 7 deletions pageserver/src/tenant/timeline.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3015,16 +3015,19 @@ impl Timeline {
// Sync it to disk.
//
// We must also fsync the timeline dir to ensure the directory entries for
// new layer files are durable
// new layer files are durable.
//
// NB: timeline dir must be synced _after_ the file contents are durable.
// So, two separate fsyncs are required, they mustn't be batched.
//
// TODO: If we're running inside 'flush_frozen_layers' and there are multiple
// files to flush, it might be better to first write them all, and then fsync
// them all in parallel.

// First sync the delta layer. We still use par_fsync here to keep everything consistent. Feel free to replace
// this with a single fsync in future refactors.
// files to flush, the fsync overhead can be reduces as follows:
// 1. write them all to temporary file names
// 2. fsync them
// 3. rename to the final name
// 4. fsync the parent directory.
// Note that (1),(2),(3) today happen inside write_to_disk().
par_fsync::par_fsync(&[new_delta_path.clone()]).context("fsync of delta layer")?;
// Then sync the parent directory.
par_fsync::par_fsync(&[self_clone
.conf
.timeline_path(&self_clone.timeline_id, &self_clone.tenant_id)])
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