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Fix #917 (Lite) — base FinOps memory recommendation on 7-day P95 #920

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erikdarlingdata merged 1 commit into from
May 2, 2026
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Fix #917 (Lite) — base FinOps memory recommendation on 7-day P95 #920

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104 changes: 82 additions & 22 deletions Lite/Services/LocalDataService.FinOps.Recommendations.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -193,23 +193,55 @@ IF @sql <> N''
// 3. Memory right-sizing score (from DuckDB)
try
{
/* Use P95 of total_server_memory_mb (perfmon "Total Server Memory" — the
full set of memory SQL has committed) over 7 days, not a single-sample
snapshot of buffer_pool_mb (data cache only). The earlier version
could fire right after a service restart or on servers where plan
cache / workspace memory dominates, falsely showing "buffer pool 0%". */
var util = await GetUtilizationEfficiencyAsync(serverId);
if (util != null && util.PhysicalMemoryMb > 8192)
{
var bpRatio = util.PhysicalMemoryMb > 0 ? (decimal)util.BufferPoolMb / util.PhysicalMemoryMb : 0m;
if (bpRatio < 0.50m)
int p95Mb = 0;
long sampleCount = 0;
using (var conn = await OpenConnectionAsync())
using (var cmd = conn.CreateCommand())
{
var targetMb = Math.Max(8192, util.BufferPoolMb * 2);
recommendations.Add(new RecommendationRow
cmd.CommandText = @"
SELECT
PERCENTILE_CONT(0.95) WITHIN GROUP (ORDER BY total_server_memory_mb) AS p95_mb,
COUNT(*) AS sample_count
FROM v_memory_stats
WHERE server_id = $1
AND collection_time >= $2";
cmd.Parameters.Add(new DuckDBParameter { Value = serverId });
cmd.Parameters.Add(new DuckDBParameter { Value = DateTime.UtcNow.AddDays(-7) });

using var reader = await cmd.ExecuteReaderAsync();
if (await reader.ReadAsync())
{
Category = "Memory",
Severity = bpRatio < 0.30m ? "High" : "Medium",
Confidence = "Medium",
Finding = $"Memory over-provisioned (buffer pool uses {bpRatio:P0} of {util.PhysicalMemoryMb / 1024}GB RAM)",
Detail = $"Buffer pool is {util.BufferPoolMb:N0} MB out of {util.PhysicalMemoryMb:N0} MB physical RAM ({bpRatio:P0} utilization). " +
$"Consider reducing to ~{targetMb / 1024}GB.",
EstMonthlySavings = monthlyCost > 0 ? monthlyCost * (1m - (decimal)targetMb / util.PhysicalMemoryMb) * 0.30m : null
});
p95Mb = reader.IsDBNull(0) ? 0 : Convert.ToInt32(reader.GetValue(0));
sampleCount = reader.IsDBNull(1) ? 0L : ToInt64(reader.GetValue(1));
}
}

// Need at least ~1 day of samples (one per minute baseline) to trust the P95
if (sampleCount >= 500)
{
var memRatio = (decimal)p95Mb / util.PhysicalMemoryMb;
if (memRatio < 0.50m)
{
var targetMb = Math.Max(8192, p95Mb * 2);
recommendations.Add(new RecommendationRow
{
Category = "Memory",
Severity = memRatio < 0.30m ? "High" : "Medium",
Confidence = "Medium",
Finding = $"Memory over-provisioned (P95 SQL memory uses {memRatio:P0} of {util.PhysicalMemoryMb / 1024}GB RAM)",
Detail = $"P95 SQL Server memory over 7 days is {p95Mb:N0} MB out of {util.PhysicalMemoryMb:N0} MB physical RAM ({memRatio:P0} utilization). " +
$"Consider reducing to ~{targetMb / 1024}GB.",
EstMonthlySavings = monthlyCost > 0 ? monthlyCost * (1m - (decimal)targetMb / util.PhysicalMemoryMb) * 0.30m : null
});
}
}
}
}
Expand Down Expand Up @@ -439,11 +471,16 @@ ORDER BY times_ran_long DESC
var vmUtil = await GetUtilizationEfficiencyAsync(serverId);
if (vmUtil != null)
{
// CPU data comes from 24-hour window in GetUtilizationEfficiencyAsync.
// For a 7-day P95 we query DuckDB directly.
/* Memory side previously read util.BufferPoolMb (a single snapshot
of perfmon "Database Cache Memory") — only the data-cache slice
of the buffer pool, ignoring plan cache / workspace / locks /
CLR — and could trigger right after a service restart. Now use
7-day P95 of total_server_memory_mb from v_memory_stats, the
same signal the Utilization tab shows. */
decimal p95Cpu7d = vmUtil.P95CpuPct;
int cpuCount = vmUtil.CpuCount;
int bpMb = vmUtil.BufferPoolMb;
int p95MemMb = 0;
long memSampleCount = 0;
int physMb = vmUtil.PhysicalMemoryMb;

// Try 7-day P95 from DuckDB for better accuracy
Expand All @@ -467,6 +504,29 @@ FROM v_cpu_utilization_stats
}
catch { /* fall back to 24-hour P95 */ }

try
{
using var memConn = await OpenConnectionAsync();
using var memCmd = memConn.CreateCommand();
memCmd.CommandText = @"
SELECT
PERCENTILE_CONT(0.95) WITHIN GROUP (ORDER BY total_server_memory_mb) AS p95_mb,
COUNT(*) AS sample_count
FROM v_memory_stats
WHERE server_id = $1
AND collection_time >= $2";
memCmd.Parameters.Add(new DuckDBParameter { Value = serverId });
memCmd.Parameters.Add(new DuckDBParameter { Value = DateTime.UtcNow.AddDays(-7) });

using var memReader = await memCmd.ExecuteReaderAsync();
if (await memReader.ReadAsync())
{
p95MemMb = memReader.IsDBNull(0) ? 0 : Convert.ToInt32(memReader.GetValue(0));
memSampleCount = memReader.IsDBNull(1) ? 0L : ToInt64(memReader.GetValue(1));
}
}
catch { /* if we cannot get 7-day P95 memory, skip the memory prescription */ }

// CPU prescription: only if >= 4 cores
if (cpuCount >= 4)
{
Expand All @@ -493,14 +553,14 @@ FROM v_cpu_utilization_stats
}
}

// Memory prescription: only if >= 4096 MB
if (physMb >= 4096 && physMb > 0)
// Memory prescription: needs >= 4 GB physical and at least ~1 day of samples
if (physMb >= 4096 && physMb > 0 && memSampleCount >= 500)
{
var bpRatio = (decimal)bpMb / physMb;
var memRatio = (decimal)p95MemMb / physMb;
int targetMb = 0;
if (bpRatio < 0.25m)
if (memRatio < 0.25m)
targetMb = Math.Max(4096, physMb / 4);
else if (bpRatio < 0.40m)
else if (memRatio < 0.40m)
targetMb = Math.Max(4096, physMb / 2);

if (targetMb > 0 && targetMb < physMb)
Expand All @@ -510,8 +570,8 @@ FROM v_cpu_utilization_stats
Category = "Hardware",
Severity = "Medium",
Confidence = "Medium",
Finding = $"Memory: reduce from {physMb / 1024}GB to {targetMb / 1024}GB (buffer pool uses {bpRatio:P0})",
Detail = $"Buffer pool is using {bpMb:N0} MB of {physMb:N0} MB physical RAM ({bpRatio:P0}). " +
Finding = $"Memory: reduce from {physMb / 1024}GB to {targetMb / 1024}GB (P95 SQL memory uses {memRatio:P0})",
Detail = $"P95 SQL Server memory over 7 days is {p95MemMb:N0} MB of {physMb:N0} MB physical RAM ({memRatio:P0}). " +
$"Reducing to {targetMb / 1024}GB would still leave headroom.",
EstMonthlySavings = monthlyCost > 0
? monthlyCost * (1m - (decimal)targetMb / physMb) * 0.30m
Expand Down
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