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gxs: adapt the warm-up slice size to a fixed per-slice time budget

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A fixed 4096-row slice held mDbMutex for ~10 s on a cold large-row
database (23492 forum metas warmed in 6 slices of ~10 s each), stalling
single-group readers for that long -- the very stall the background scan
exists to avoid. Start at 256 rows and rescale each slice towards a
250 ms target, clamped to [64, 4096] rows.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
jolavillette 2026-08-05 13:53:52 +02:00
parent b26e445273
commit 4a61ccee00
1 changed files with 29 additions and 4 deletions
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33
src/gxs/rsdataservice.cc
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@ -1328,7 +1328,15 @@ void RsDataService::msgMetaWarmupThreadBody()
// a deletion) are covered; until the scan completes, cold groups keep
// being served by the indexed per-group query.
static const uint32_t WARMUP_SLICE_ROWS = 4096;
// The slice size adapts so that one slice -- hence one mDbMutex hold --
// stays around WARMUP_SLICE_TARGET_MS. With a fixed row count, a cold
// slice of a large-row database was measured at ~10 s, which is exactly
// the reader stall this thread exists to avoid.
static const int64_t WARMUP_SLICE_TARGET_MS = 250;
static const uint32_t WARMUP_SLICE_MIN_ROWS = 64;
static const uint32_t WARMUP_SLICE_MAX_ROWS = 4096;
uint32_t slice_rows = 256;
std::list<std::string> columns(mMsgMetaColumns);
columns.push_front("rowid");
@ -1341,6 +1349,8 @@ void RsDataService::msgMetaWarmupThreadBody()
while(!done && !mMsgMetaWarmupStop)
{
auto slice_t0 = std::chrono::steady_clock::now();
{
RsStackMutex stack(mDbMutex);
@ -1349,7 +1359,7 @@ void RsDataService::msgMetaWarmupThreadBody()
RetroCursor* c = mDb->sqlQuery(MSG_TABLE_NAME, columns,
"rowid > " + std::to_string(last_rowid),
"rowid LIMIT " + std::to_string(WARMUP_SLICE_ROWS));
"rowid LIMIT " + std::to_string(slice_rows));
if(!c)
{
@ -1378,7 +1388,7 @@ void RsDataService::msgMetaWarmupThreadBody()
total_rows += n_rows;
++n_slices;
if(n_rows < WARMUP_SLICE_ROWS)
if(n_rows < slice_rows)
{
// Last slice. Every group of this database now holds all its
// metas, including the ones that have no message at all and
@ -1391,9 +1401,24 @@ void RsDataService::msgMetaWarmupThreadBody()
}
}
// Let the readers waiting on mDbMutex in between two slices.
if(!done)
{
// Rescale the next slice towards the per-slice time target.
int64_t slice_ms = std::chrono::duration_cast<std::chrono::milliseconds>(
std::chrono::steady_clock::now() - slice_t0).count();
if(slice_ms > 0)
{
uint64_t next = (uint64_t)slice_rows * WARMUP_SLICE_TARGET_MS / slice_ms;
slice_rows = (uint32_t)std::min<uint64_t>(WARMUP_SLICE_MAX_ROWS,
std::max<uint64_t>(WARMUP_SLICE_MIN_ROWS, next));
}
else
slice_rows = WARMUP_SLICE_MAX_ROWS;
// Let the readers waiting on mDbMutex in between two slices.
std::this_thread::sleep_for(std::chrono::milliseconds(20));
}
}
if(done)