1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
|
/*-------------------------------------------------------------------------
*
* buf_init.c
* buffer manager initialization routines
*
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/buf_init.c,v 1.76 2005/08/20 23:26:17 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "storage/bufmgr.h"
#include "storage/buf_internals.h"
BufferDesc *BufferDescriptors;
char *BufferBlocks;
int32 *PrivateRefCount;
/* statistics counters */
long int ReadBufferCount;
long int ReadLocalBufferCount;
long int BufferHitCount;
long int LocalBufferHitCount;
long int BufferFlushCount;
long int LocalBufferFlushCount;
/*
* Data Structures:
* buffers live in a freelist and a lookup data structure.
*
*
* Buffer Lookup:
* Two important notes. First, the buffer has to be
* available for lookup BEFORE an IO begins. Otherwise
* a second process trying to read the buffer will
* allocate its own copy and the buffer pool will
* become inconsistent.
*
* Buffer Replacement:
* see freelist.c. A buffer cannot be replaced while in
* use either by data manager or during IO.
*
*
* Synchronization/Locking:
*
* IO_IN_PROGRESS -- this is a flag in the buffer descriptor.
* It must be set when an IO is initiated and cleared at
* the end of the IO. It is there to make sure that one
* process doesn't start to use a buffer while another is
* faulting it in. see WaitIO and related routines.
*
* refcount -- Counts the number of processes holding pins on a buffer.
* A buffer is pinned during IO and immediately after a BufferAlloc().
* Pins must be released before end of transaction.
*
* PrivateRefCount -- Each buffer also has a private refcount that keeps
* track of the number of times the buffer is pinned in the current
* process. This is used for two purposes: first, if we pin a
* a buffer more than once, we only need to change the shared refcount
* once, thus only lock the shared state once; second, when a transaction
* aborts, it should only unpin the buffers exactly the number of times it
* has pinned them, so that it will not blow away buffers of another
* backend.
*/
/*
* Initialize shared buffer pool
*
* This is called once during shared-memory initialization (either in the
* postmaster, or in a standalone backend).
*/
void
InitBufferPool(void)
{
bool foundBufs,
foundDescs;
BufferDescriptors = (BufferDesc *)
ShmemInitStruct("Buffer Descriptors",
NBuffers * sizeof(BufferDesc), &foundDescs);
BufferBlocks = (char *)
ShmemInitStruct("Buffer Blocks",
NBuffers * (Size) BLCKSZ, &foundBufs);
if (foundDescs || foundBufs)
{
/* both should be present or neither */
Assert(foundDescs && foundBufs);
/* note: this path is only taken in EXEC_BACKEND case */
}
else
{
BufferDesc *buf;
int i;
buf = BufferDescriptors;
/*
* Initialize all the buffer headers.
*/
for (i = 0; i < NBuffers; buf++, i++)
{
CLEAR_BUFFERTAG(buf->tag);
buf->flags = 0;
buf->usage_count = 0;
buf->refcount = 0;
buf->wait_backend_pid = 0;
SpinLockInit(&buf->buf_hdr_lock);
buf->buf_id = i;
/*
* Initially link all the buffers together as unused.
* Subsequent management of this list is done by freelist.c.
*/
buf->freeNext = i + 1;
buf->io_in_progress_lock = LWLockAssign();
buf->content_lock = LWLockAssign();
}
/* Correct last entry of linked list */
BufferDescriptors[NBuffers - 1].freeNext = FREENEXT_END_OF_LIST;
}
/* Init other shared buffer-management stuff */
StrategyInitialize(!foundDescs);
}
/*
* Initialize access to shared buffer pool
*
* This is called during backend startup (whether standalone or under the
* postmaster). It sets up for this backend's access to the already-existing
* buffer pool.
*
* NB: this is called before InitProcess(), so we do not have a PGPROC and
* cannot do LWLockAcquire; hence we can't actually access stuff in
* shared memory yet. We are only initializing local data here.
* (See also InitBufferPoolBackend, over in bufmgr.c.)
*/
void
InitBufferPoolAccess(void)
{
/*
* Allocate and zero local arrays of per-buffer info.
*/
PrivateRefCount = (int32 *) calloc(NBuffers, sizeof(int32));
if (!PrivateRefCount)
ereport(FATAL,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of memory")));
}
/*
* BufferShmemSize
*
* compute the size of shared memory for the buffer pool including
* data pages, buffer descriptors, hash tables, etc.
*/
Size
BufferShmemSize(void)
{
Size size = 0;
/* size of buffer descriptors */
size = add_size(size, mul_size(NBuffers, sizeof(BufferDesc)));
/* size of data pages */
size = add_size(size, mul_size(NBuffers, BLCKSZ));
/* size of stuff controlled by freelist.c */
size = add_size(size, StrategyShmemSize());
return size;
}
|
