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Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>
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György Krajcsovits 2026-01-30 11:31:54 +01:00
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commit 6133dd5f3e
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5
tsdb/chunkenc/xoroptst.go
View file

@ -56,9 +56,8 @@ func readSTHeader(b []byte) (firstSTKnown bool, firstSTChangeOn uint8) {
return firstSTKnown, b[0] & mask
}
// XorOptSTChunk holds encoded sample data:
// 2B(numSamples), 1B(stHeader), ?varint(st), varint(t), xor(v), ?varuint(stDelta), varuint(tDelta), xor(v), ?classicvarbitint(stDod), classicvarbitint(tDod), xor(v), ...
// stHeader: 1b(firstSTKnown), 7b(firstSTChangeOn).
// XorOptSTChunk holds XOR enncoded samples with optional start time (ST)
// per chunk or per sample. See tsdb/docs/format/chunks.md for details.
type XorOptSTChunk struct {
b bstream
}

51
tsdb/docs/format/chunks.md
View file

@ -65,6 +65,57 @@ Notes:
* `padding` of 0 to 7 bits so that the whole chunk data is byte-aligned.
* The chunk can have as few as one sample, i.e. `ts_1`, `v_1`, etc. are optional.
## XOR chunk data with start timestamp
This is experimental, related to supporting delta temporality metrics.
Subject to change.
The format is similar to XOR chunk data, except there's an additional one byte
start time (ST) header and optional start time values, delta, delta of deltas.
```
┌──────────────────────┬───────────────────┬────────────────┬───────────────────────────────┬─-
│ num_samples <uint16> │ st_header <uint8> | ?st_0 <varint> | ts_0 <varint> │ v_0 <float64> │
└──────────────────────┴───────────────────┴────────────────┴───────────────────────────────┴─-
-──────────────────────┬──────────────────────┬──────────────────────┬─-
?st_1_delta <varint> | ts_1_delta <uvarint> │ v_1_xor <varbit_xor> │
-──────────────────────┴──────────────────────┴──────────────────────┴─-
-──────────────────────┬──────────────────────┬──────────────────────┬─────┬─-
?st_2_dod <varbit_ts> | ts_2_dod <varbit_ts> │ v_2_xor <varbit_xor> │ ... │
-──────────────────────┴──────────────────────┴──────────────────────┴─────┴─-
-──────────────────────┬──────────────────────┬──────────────────────┬──────────────────┐
?st_n_dod <varbit_ts> | ts_n_dod <varbit_ts> │ v_n_xor <varbit_xor> │ padding <x bits> │
-──────────────────────┴──────────────────────┴──────────────────────┴──────────────────┘
```
### Notes
In addition to the notes from [XOR chunk data](#xor-chunk-data).
* We use `st_i_dod` and `st_i` interchangeably when `i>1` in these notes.
* `st_header` is one byte:
```
┌───────────────────────┬───────────────────────┐
│ first_st_known<1 bit> | st_changed_on<7 bits> │
└───────────────────────┴───────────────────────┘
```
where the highest bit `first_st_known` indicates if `st_0` is present or not.
If the lower 7bits `st_changed_on` is 0, no `st_i (i>0)` is present.
Otherwise `st_i (i>=st_changed_on>)` is present, while
`st_i (0<i<st_changed_on)` is not present.
Due to the 7 bit limitation, once a chunk has at least 127 samples,
`st_changed_on` is set to 127 (0xEF) and the 127th and further samples will
have `st_i` present.
* `st_0` is encoded as a `varint` if present.
* `st_1` is encoded as a `varint` delta from `st_0` (or from 0 if `st_0` is not
present).
* `st_i_dod` aka `st_i (i>1)` is encoded as a `varbit_ts` "delta of delta" from
`st_i-1` (or from 0 if `st_i-1` is not present).
## Histogram chunk data
```