Meh, of course I forgot to actually attach the patch.
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>From 8f207693faa65e65e8a1e5e894c2ad96ad1f3cea Mon Sep 17 00:00:00 2001
From: Tomas Vondra <to...@pgaddict.com>
Date: Mon, 28 Dec 2015 14:20:17 +0100
Subject: [PATCH 1/2] extend the HyperLogLog API a bit by adding two more
methods
- initHyperLogLogError (initialize the counter for error rate)
- freeHyperLogLog (release the memory allocated for counter state)
---
src/backend/lib/hyperloglog.c | 29 +++++++++++++++++++++++++++++
src/include/lib/hyperloglog.h | 2 ++
2 files changed, 31 insertions(+)
diff --git a/src/backend/lib/hyperloglog.c b/src/backend/lib/hyperloglog.c
index 718afb8..2949a8d 100644
--- a/src/backend/lib/hyperloglog.c
+++ b/src/backend/lib/hyperloglog.c
@@ -108,6 +108,35 @@ initHyperLogLog(hyperLogLogState *cState, uint8 bwidth)
}
/*
+ * Initialize HyperLogLog track state
+ */
+void
+initHyperLogLogError(hyperLogLogState *cState, double error)
+{
+ uint8 bwidth = 4;
+
+ while (bwidth < 16)
+ {
+ double m = (Size)1 << bwidth;
+ if (1.04 / sqrt(m) < error)
+ break;
+ bwidth++;
+ }
+
+ initHyperLogLog(cState, bwidth);
+}
+
+/*
+ * Free HyperLogLog track state
+ */
+void
+freeHyperLogLog(hyperLogLogState *cState)
+{
+ Assert(cState->hashesArr != NULL);
+ pfree(cState->hashesArr);
+}
+
+/*
* Adds element to the estimator, from caller-supplied hash.
*
* It is critical that the hash value passed be an actual hash value, typically
diff --git a/src/include/lib/hyperloglog.h b/src/include/lib/hyperloglog.h
index fd8280c..004490a 100644
--- a/src/include/lib/hyperloglog.h
+++ b/src/include/lib/hyperloglog.h
@@ -60,8 +60,10 @@ typedef struct hyperLogLogState
} hyperLogLogState;
extern void initHyperLogLog(hyperLogLogState *cState, uint8 bwidth);
+extern void initHyperLogLogError(hyperLogLogState *cState, double error);
extern void addHyperLogLog(hyperLogLogState *cState, uint32 hash);
extern double estimateHyperLogLog(hyperLogLogState *cState);
extern void mergeHyperLogLog(hyperLogLogState *cState, const hyperLogLogState *oState);
+extern void freeHyperLogLog(hyperLogLogState *cState);
#endif /* HYPERLOGLOG_H */
--
2.1.0
--
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