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Commit d65522a

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tglsfdctglsfdc
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Upgrade localbuf.c to use a hash table instead of linear search to
find already-allocated local buffers. This is the last obstacle in the way of setting NLocBuffer to something reasonably large.
1 parent 2e62908 commit d65522a

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1 file changed

+100
-46
lines changed

1 file changed

+100
-46
lines changed

‎src/backend/storage/buffer/localbuf.c‎

Lines changed: 100 additions & 46 deletions
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@
99
*
1010
*
1111
* IDENTIFICATION
12-
* $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.64 2005/03/18 16:16:09 tgl Exp $
12+
* $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.65 2005/03/19 17:39:43 tgl Exp $
1313
*
1414
*-------------------------------------------------------------------------
1515
*/
@@ -18,29 +18,37 @@
1818
#include "storage/buf_internals.h"
1919
#include "storage/bufmgr.h"
2020
#include "storage/smgr.h"
21-
#include "utils/relcache.h"
21+
#include "utils/memutils.h"
2222
#include "utils/resowner.h"
2323

2424

2525
/*#define LBDEBUG*/
2626

27+
/* entry for buffer lookup hashtable */
28+
typedef struct
29+
{
30+
BufferTag key; /* Tag of a disk page */
31+
int id; /* Associated local buffer's index */
32+
} LocalBufferLookupEnt;
33+
2734
/* Note: this macro only works on local buffers, not shared ones! */
2835
#define LocalBufHdrGetBlock(bufHdr) \
2936
LocalBufferBlockPointers[-((bufHdr)->buf_id + 2)]
3037

31-
/* should be a GUC parameter some day */
32-
int NLocBuffer = 64;
38+
int NLocBuffer = 0; /* until buffers are initialized */
3339

3440
BufferDesc *LocalBufferDescriptors = NULL;
3541
Block *LocalBufferBlockPointers = NULL;
3642
int32 *LocalRefCount = NULL;
3743

3844
static int nextFreeLocalBuf = 0;
3945

46+
static HTAB *LocalBufHash = NULL;
47+
4048

4149
/*
4250
* LocalBufferAlloc -
43-
* allocate a local buffer. We do round robin allocation for now.
51+
* Find or create a local buffer for the given page of the given relation.
4452
*
4553
* API is similar to bufmgr.c's BufferAlloc, except that we do not need
4654
* to do any locking since this is all local. Also, IO_IN_PROGRESS
@@ -50,35 +58,39 @@ BufferDesc *
5058
LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
5159
{
5260
BufferTag newTag; /* identity of requested block */
53-
int i;
54-
int trycounter;
61+
LocalBufferLookupEnt *hresult;
5562
BufferDesc *bufHdr;
63+
int b;
64+
int trycounter;
65+
bool found;
5666

5767
INIT_BUFFERTAG(newTag, reln, blockNum);
5868

59-
/* a low tech search for now -- should use a hashtable */
60-
for (i = 0; i < NLocBuffer; i++)
69+
/* See if the desired buffer already exists */
70+
hresult = (LocalBufferLookupEnt *)
71+
hash_search(LocalBufHash, (void *) &newTag, HASH_FIND, NULL);
72+
73+
if (hresult)
6174
{
62-
bufHdr = &LocalBufferDescriptors[i];
63-
if (BUFFERTAGS_EQUAL(bufHdr->tag, newTag))
64-
{
75+
b = hresult->id;
76+
bufHdr = &LocalBufferDescriptors[b];
77+
Assert(BUFFERTAGS_EQUAL(bufHdr->tag, newTag));
6578
#ifdef LBDEBUG
66-
fprintf(stderr, "LB ALLOC (%u,%d) %d\n",
67-
RelationGetRelid(reln), blockNum, -i - 1);
79+
fprintf(stderr, "LB ALLOC (%u,%d) %d\n",
80+
RelationGetRelid(reln), blockNum, -b - 1);
6881
#endif
6982

70-
LocalRefCount[i]++;
71-
ResourceOwnerRememberBuffer(CurrentResourceOwner,
72-
BufferDescriptorGetBuffer(bufHdr));
73-
if (bufHdr->flags & BM_VALID)
74-
*foundPtr = TRUE;
75-
else
76-
{
77-
/* Previous read attempt must have failed; try again */
78-
*foundPtr = FALSE;
79-
}
80-
return bufHdr;
83+
LocalRefCount[b]++;
84+
ResourceOwnerRememberBuffer(CurrentResourceOwner,
85+
BufferDescriptorGetBuffer(bufHdr));
86+
if (bufHdr->flags & BM_VALID)
87+
*foundPtr = TRUE;
88+
else
89+
{
90+
/* Previous read attempt must have failed; try again */
91+
*foundPtr = FALSE;
8192
}
93+
return bufHdr;
8294
}
8395

8496
#ifdef LBDEBUG
@@ -93,7 +105,7 @@ LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
93105
trycounter = NLocBuffer;
94106
for (;;)
95107
{
96-
int b = nextFreeLocalBuf;
108+
b = nextFreeLocalBuf;
97109

98110
if (++nextFreeLocalBuf >= NLocBuffer)
99111
nextFreeLocalBuf = 0;
@@ -136,31 +148,50 @@ LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
136148
(char *) LocalBufHdrGetBlock(bufHdr),
137149
true);
138150

151+
/* Mark not-dirty now in case we error out below */
152+
bufHdr->flags &= ~BM_DIRTY;
153+
139154
LocalBufferFlushCount++;
140155
}
141156

142157
/*
143158
* lazy memory allocation: allocate space on first use of a buffer.
144-
*
145-
* Note this path cannot be taken for a buffer that was previously in
146-
* use, so it's okay to do it (and possibly error out) before marking
147-
* the buffer as not dirty.
148159
*/
149160
if (LocalBufHdrGetBlock(bufHdr) == NULL)
150161
{
151-
char *data = (char *) malloc(BLCKSZ);
162+
char *data;
152163

153-
if (data == NULL)
154-
ereport(ERROR,
155-
(errcode(ERRCODE_OUT_OF_MEMORY),
156-
errmsg("out of memory")));
164+
data = (char *) MemoryContextAlloc(TopMemoryContext, BLCKSZ);
157165

158-
/*
159-
* Set pointer for use by BufferGetBlock() macro.
160-
*/
166+
/* Set pointer for use by BufferGetBlock() macro */
161167
LocalBufHdrGetBlock(bufHdr) = (Block) data;
162168
}
163169

170+
/*
171+
* Update the hash table: remove old entry, if any, and make new one.
172+
*/
173+
if (bufHdr->flags & BM_TAG_VALID)
174+
{
175+
hresult = (LocalBufferLookupEnt *)
176+
hash_search(LocalBufHash, (void *) &bufHdr->tag,
177+
HASH_REMOVE, NULL);
178+
if (!hresult) /* shouldn't happen */
179+
elog(ERROR, "local buffer hash table corrupted");
180+
/* mark buffer invalid just in case hash insert fails */
181+
CLEAR_BUFFERTAG(bufHdr->tag);
182+
bufHdr->flags &= ~(BM_VALID | BM_TAG_VALID);
183+
}
184+
185+
hresult = (LocalBufferLookupEnt *)
186+
hash_search(LocalBufHash, (void *) &newTag, HASH_ENTER, &found);
187+
if (!hresult)
188+
ereport(ERROR,
189+
(errcode(ERRCODE_OUT_OF_MEMORY),
190+
errmsg("out of memory")));
191+
if (found) /* shouldn't happen */
192+
elog(ERROR, "local buffer hash table corrupted");
193+
hresult->id = b;
194+
164195
/*
165196
* it's all ours now.
166197
*/
@@ -215,20 +246,39 @@ WriteLocalBuffer(Buffer buffer, bool release)
215246
void
216247
InitLocalBuffer(void)
217248
{
249+
int nbufs = 64; /* should be from a GUC var */
250+
HASHCTL info;
218251
int i;
219252

220-
/*
221-
* these aren't going away. I'm not gonna use palloc.
222-
*/
253+
/* Create the lookup hash table */
254+
MemSet(&info, 0, sizeof(info));
255+
info.keysize = sizeof(BufferTag);
256+
info.entrysize = sizeof(LocalBufferLookupEnt);
257+
info.hash = tag_hash;
258+
259+
LocalBufHash = hash_create("Local Buffer Lookup Table",
260+
nbufs,
261+
&info,
262+
HASH_ELEM | HASH_FUNCTION);
263+
264+
if (!LocalBufHash)
265+
elog(ERROR, "could not initialize local buffer hash table");
266+
267+
/* Allocate and zero buffer headers and auxiliary arrays */
223268
LocalBufferDescriptors = (BufferDesc *)
224-
calloc(NLocBuffer, sizeof(*LocalBufferDescriptors));
269+
MemoryContextAllocZero(TopMemoryContext,
270+
nbufs * sizeof(BufferDesc));
225271
LocalBufferBlockPointers = (Block *)
226-
calloc(NLocBuffer, sizeof(*LocalBufferBlockPointers));
272+
MemoryContextAllocZero(TopMemoryContext,
273+
nbufs * sizeof(Block));
227274
LocalRefCount = (int32 *)
228-
calloc(NLocBuffer, sizeof(*LocalRefCount));
275+
MemoryContextAllocZero(TopMemoryContext,
276+
nbufs * sizeof(int32));
277+
229278
nextFreeLocalBuf = 0;
230279

231-
for (i = 0; i < NLocBuffer; i++)
280+
/* initialize fields that need to start off nonzero */
281+
for (i = 0; i < nbufs; i++)
232282
{
233283
BufferDesc *buf = &LocalBufferDescriptors[i];
234284

@@ -240,6 +290,9 @@ InitLocalBuffer(void)
240290
*/
241291
buf->buf_id = -i - 2;
242292
}
293+
294+
/* Initialization done, mark buffers allocated */
295+
NLocBuffer = nbufs;
243296
}
244297

245298
/*
@@ -271,5 +324,6 @@ void
271324
AtProcExit_LocalBuffers(void)
272325
{
273326
/* just zero the refcounts ... */
274-
MemSet(LocalRefCount, 0, NLocBuffer * sizeof(*LocalRefCount));
327+
if (LocalRefCount)
328+
MemSet(LocalRefCount, 0, NLocBuffer * sizeof(*LocalRefCount));
275329
}

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