Thread
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pg_freespacemap question
Tatsuo Ishii <ishii@sraoss.co.jp> — 2006-03-07T14:09:56Z
Hi, I tried pg_freespacemap and found strange result: test=# select * from pg_freespacemap where blockfreebytes = 0; blockid | relfilenode | reltablespace | reldatabase | relblocknumber | blockfreebytes ---------+-------------+---------------+-------------+----------------+---------------- 25 | 2619 | 1663 | 16403 | 0 | 0 63 | 2619 | 1663 | 16384 | 10 | 0 (2 rows) Is it possible that a free space map entry has 0 blockfreebytes? -- Tatsuo Ishii SRA OSS, Inc. Japan -
Re: pg_freespacemap question
Peter Eisentraut <peter_e@gmx.net> — 2006-03-07T14:29:58Z
Am Dienstag, 7. März 2006 15:09 schrieb Tatsuo Ishii: > test=# select * from pg_freespacemap where blockfreebytes = 0; > blockid | relfilenode | reltablespace | reldatabase | relblocknumber | blockfreebytes > ---------+-------------+---------------+-------------+----------------+---------------- > 25 | 2619 | 1663 | 16403 | 0 | 0 > 63 | 2619 | 1663 | 16384 | 10 | 0 > (2 rows) I've never heard of this thing before but is this column order supposed to make sense? -- Peter Eisentraut http://developer.postgresql.org/~petere/
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Re: pg_freespacemap question
Alvaro Herrera <alvherre@commandprompt.com> — 2006-03-07T14:37:51Z
Peter Eisentraut wrote: > Am Dienstag, 7. März 2006 15:09 schrieb Tatsuo Ishii: > > test=# select * from pg_freespacemap where blockfreebytes = 0; > > blockid | relfilenode | reltablespace | reldatabase | relblocknumber | blockfreebytes > > ---------+-------------+---------------+-------------+----------------+---------------- > > 25 | 2619 | 1663 | 16403 | 0 | 0 > > 63 | 2619 | 1663 | 16384 | 10 | 0 > > (2 rows) > > I've never heard of this thing before but is this column order supposed to make sense? I have another question -- why is the view showing relfilenode and reltablespace? I imagine it should be showing the relation Oid instead. And what is this "blockid" thing? -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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Re: pg_freespacemap question
Tatsuo Ishii <ishii@sraoss.co.jp> — 2006-03-07T15:37:44Z
> Peter Eisentraut wrote: > > Am Dienstag, 7. März 2006 15:09 schrieb Tatsuo Ishii: > > > test=# select * from pg_freespacemap where blockfreebytes = 0; > > > blockid | relfilenode | reltablespace | reldatabase | relblocknumber | blockfreebytes > > > ---------+-------------+---------------+-------------+----------------+---------------- > > > 25 | 2619 | 1663 | 16403 | 0 | 0 > > > 63 | 2619 | 1663 | 16384 | 10 | 0 > > > (2 rows) > > > > I've never heard of this thing before but is this column order supposed to make sense? > > I have another question -- why is the view showing relfilenode and > reltablespace? I imagine it should be showing the relation Oid instead. I guess that's because FSM keeps those info, not relation oid. > And what is this "blockid" thing? from README.pg_freespacemap: blockid | | Id, 1.. max_fsm_pages BTW, I found the answer to my question myself by reading the source code: if that's an index, then blockfreebytes is explicitly set to 0. I suggest that this should be noted in the README and in this case blockfreebytes is better to set to NULL, rather than 0. -- Tatsuo Ishii SRA OSS, Inc. Japan
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Re: pg_freespacemap question
Tom Lane <tgl@sss.pgh.pa.us> — 2006-03-07T15:44:49Z
Tatsuo Ishii <ishii@sraoss.co.jp> writes: >> Peter Eisentraut wrote: >> I have another question -- why is the view showing relfilenode and >> reltablespace? I imagine it should be showing the relation Oid instead. > I guess that's because FSM keeps those info, not relation oid. Right, which is correct because free space is associated with physical files not logical relations. (TRUNCATE, CLUSTER, etc will completely change the freespace situation for a rel, but they don't change its OID.) I do agree with the comment that the column order seems nonintuitive; I'd expect database/tablespace/relfilenode/blocknumber, or possibly tablespace first. The names used for the columns could do with reconsideration. And I don't see the point of the blockid column at all. regards, tom lane
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Re: pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-07T23:24:22Z
Tatsuo Ishii wrote: >>Peter Eisentraut wrote: >> >>>Am Dienstag, 7. März 2006 15:09 schrieb Tatsuo Ishii: >>> >>>>test=# select * from pg_freespacemap where blockfreebytes = 0; >>>> blockid | relfilenode | reltablespace | reldatabase | relblocknumber | blockfreebytes >>>>---------+-------------+---------------+-------------+----------------+---------------- >>>> 25 | 2619 | 1663 | 16403 | 0 | 0 >>>> 63 | 2619 | 1663 | 16384 | 10 | 0 >>>>(2 rows) >>> >>>I've never heard of this thing before but is this column order supposed to make sense? >> >>I have another question -- why is the view showing relfilenode and >>reltablespace? I imagine it should be showing the relation Oid instead. > > > I guess that's because FSM keeps those info, not relation oid. > > >>And what is this "blockid" thing? > > > from README.pg_freespacemap: > > blockid | | Id, 1.. max_fsm_pages > I put that in as a bit of a sanity check - to see if the view was picking up all the fsm pages - guess it is a bit redundant now. > BTW, I found the answer to my question myself by reading the source > code: if that's an index, then blockfreebytes is explicitly set to 0. > I suggest that this should be noted in the README and in this case > blockfreebytes is better to set to NULL, rather than 0. > Good points! I had not noticed this test case. Probably NULL is better than zero. I'll look into making these changes! (good to see people checking the view out). Cheers Mark
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Re: pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-07T23:31:36Z
Tom Lane wrote: > Tatsuo Ishii <ishii@sraoss.co.jp> writes: > >>>Peter Eisentraut wrote: >>>I have another question -- why is the view showing relfilenode and >>>reltablespace? I imagine it should be showing the relation Oid instead. > > >>I guess that's because FSM keeps those info, not relation oid. > > > Right, which is correct because free space is associated with physical > files not logical relations. (TRUNCATE, CLUSTER, etc will completely > change the freespace situation for a rel, but they don't change its OID.) > > I do agree with the comment that the column order seems nonintuitive; > I'd expect database/tablespace/relfilenode/blocknumber, or possibly > tablespace first. The names used for the columns could do with > reconsideration. And I don't see the point of the blockid column at > all. Tom - agreed, I'll look at making these changes too! Cheers Mark
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Re: pg_freespacemap question
Tatsuo Ishii <ishii@sraoss.co.jp> — 2006-03-07T23:42:13Z
> > BTW, I found the answer to my question myself by reading the source > > code: if that's an index, then blockfreebytes is explicitly set to 0. > > I suggest that this should be noted in the README and in this case > > blockfreebytes is better to set to NULL, rather than 0. > > > > Good points! I had not noticed this test case. Probably NULL is better > than zero. Just for curiousity, why FSM gathers info for indexes? I thought FSM is only good for tables. -- Tatsuo Ishii SRA OSS, Inc. Japan
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Re: pg_freespacemap question
Alvaro Herrera <alvherre@commandprompt.com> — 2006-03-07T23:49:24Z
Tatsuo Ishii wrote: > Just for curiousity, why FSM gathers info for indexes? I thought FSM > is only good for tables. It's part of the implementation of the page-recycling algorithm for btrees Tom did for 7.4. When a btree page is empty after a vacuum, it's entered in the free space map. When a page is split, the new page is taken from the FSM (or the relation is extended if there isn't any.) That's why the bytes-free number is zero: when a btree page makes it into the FSM, we are sure it's completely empty. -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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Re: pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-08T04:47:50Z
Mark Kirkwood wrote: > Tatsuo Ishii wrote: > >> BTW, I found the answer to my question myself by reading the source >> code: if that's an index, then blockfreebytes is explicitly set to 0. >> I suggest that this should be noted in the README and in this case >> blockfreebytes is better to set to NULL, rather than 0. >> > > Good points! I had not noticed this test case. Probably NULL is better > than zero. > Would setting it to 'BLCKSZ - (fixed index header stuff)' be better, since the btree page is empty? (I'll have to read up on how to calculate the header stuff!). regards Mark
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Re: pg_freespacemap question
Tom Lane <tgl@sss.pgh.pa.us> — 2006-03-08T15:27:48Z
Mark Kirkwood <markir@paradise.net.nz> writes: >> Good points! I had not noticed this test case. Probably NULL is better > Would setting it to 'BLCKSZ - (fixed index header stuff)' be better, No, I don't think so, because that will just make it harder to recognize what's what (remember that BLCKSZ isn't really a constant, and the index overhead is not the same for all AMs either). The point here is that for indexes the FSM tracks whole-page availability, not the amount of free space within pages. So I think NULL is a reasonable representation of that. Using NULL will make it easy to filter the results if you want to see only heap-page data or only index-page data, whereas it will be very hard to do that if the view adopts an ultimately-artificial convention about the amount of available space on an index page. regards, tom lane
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Re: pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-09T04:12:26Z
Tom Lane wrote: > Mark Kirkwood <markir@paradise.net.nz> writes: > >>>Good points! I had not noticed this test case. Probably NULL is better > > >>Would setting it to 'BLCKSZ - (fixed index header stuff)' be better, > > > No, I don't think so, because that will just make it harder to recognize > what's what (remember that BLCKSZ isn't really a constant, and the index > overhead is not the same for all AMs either). The point here is that > for indexes the FSM tracks whole-page availability, not the amount of > free space within pages. So I think NULL is a reasonable representation > of that. Using NULL will make it easy to filter the results if you want > to see only heap-page data or only index-page data, whereas it will be > very hard to do that if the view adopts an ultimately-artificial > convention about the amount of available space on an index page. > Right - after suggesting it I realized that coding the different index overhead for each possible AM would have been ... difficult :-). A patch is attached to implement the NULL free bytes and other recommendations: 1/ Index free bytes set to NULL 2/ Comment added to the README briefly mentioning the index business 3/ Columns reordered more logically 4/ 'Blockid' column removed 5/ Free bytes column renamed to just 'bytes' instead of 'blockfreebytes' Now 5/ was only hinted at, but seemed worth doing while I was there (hopefully I haven't made it too terse now....). cheers Mark
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Re: pg_freespacemap question
Tatsuo Ishii <ishii@sraoss.co.jp> — 2006-03-11T23:40:23Z
Mark, I have tried your patches and it worked great. Thanks. -- Tatsuo Ishii SRA OSS, Inc. Japan > Tom Lane wrote: > > Mark Kirkwood <markir@paradise.net.nz> writes: > > > >>>Good points! I had not noticed this test case. Probably NULL is better > > > > > >>Would setting it to 'BLCKSZ - (fixed index header stuff)' be better, > > > > > > No, I don't think so, because that will just make it harder to recognize > > what's what (remember that BLCKSZ isn't really a constant, and the index > > overhead is not the same for all AMs either). The point here is that > > for indexes the FSM tracks whole-page availability, not the amount of > > free space within pages. So I think NULL is a reasonable representation > > of that. Using NULL will make it easy to filter the results if you want > > to see only heap-page data or only index-page data, whereas it will be > > very hard to do that if the view adopts an ultimately-artificial > > convention about the amount of available space on an index page. > > > > Right - after suggesting it I realized that coding the different index > overhead for each possible AM would have been ... difficult :-). A patch > is attached to implement the NULL free bytes and other recommendations: > > 1/ Index free bytes set to NULL > 2/ Comment added to the README briefly mentioning the index business > 3/ Columns reordered more logically > 4/ 'Blockid' column removed > 5/ Free bytes column renamed to just 'bytes' instead of 'blockfreebytes' > > Now 5/ was only hinted at, but seemed worth doing while I was there > (hopefully I haven't made it too terse now....). > > cheers > > Mark >
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Re: [PATCHES] pg_freespacemap question
Tatsuo Ishii <ishii@sraoss.co.jp> — 2006-03-12T01:19:49Z
BTW, I noticed difference of outputs from pg_freespacemap and pgstattuple. I ran pgbench and inspected "accounts" table by using these tools. pg_freespacemap: sum of bytes: 250712 pgstattuple: free_space: 354880 Shouldn't they be identical? -- Tatsuo Ishii SRA OSS, Inc. Japan
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Re: [PATCHES] pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-12T22:48:33Z
Tatsuo Ishii wrote: > BTW, I noticed difference of outputs from pg_freespacemap and > pgstattuple. > > I ran pgbench and inspected "accounts" table by using these tools. > > pg_freespacemap: > sum of bytes: 250712 > > pgstattuple: > free_space: 354880 > > Shouldn't they be identical? I would have thought so - unless there are not enough pages left in the FSM... pg_freespacemap is reporting on what gets into the FSM - so provided I haven't put a bug in there somewhere (!) - we need to look at how VACUUM reports free space to the FSM.... cheers Mark
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Re: [PATCHES] pg_freespacemap question
Tom Lane <tgl@sss.pgh.pa.us> — 2006-03-13T00:43:11Z
> Tatsuo Ishii wrote: >> BTW, I noticed difference of outputs from pg_freespacemap and >> pgstattuple. >> >> I ran pgbench and inspected "accounts" table by using these tools. >> >> pg_freespacemap: >> sum of bytes: 250712 >> >> pgstattuple: >> free_space: 354880 >> >> Shouldn't they be identical? No, because (a) pgbench vacuums at the start of the run not the end, and (b) vacuum/fsm disregard pages with "uselessly small" amounts of free space (less than the average tuple size, IIRC). I do notice a rather serious shortcoming of pg_freespacemap in its current incarnation, which is that it *only* shows you the per-page free space data, and not any of the information that would let you determine what the FSM is doing to filter the raw data. The per-relation avgRequest and lastPageCount fields would be interesting for instance. Perhaps there should be a second view with one row per relation to carry the appropriate data. regards, tom lane
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Re: [PATCHES] pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-13T01:51:24Z
Tom Lane wrote: >>Tatsuo Ishii wrote: >> >>>BTW, I noticed difference of outputs from pg_freespacemap and >>>pgstattuple. >>> >>>I ran pgbench and inspected "accounts" table by using these tools. >>> >>>pg_freespacemap: >>>sum of bytes: 250712 >>> >>>pgstattuple: >>>free_space: 354880 >>> >>>Shouldn't they be identical? > > > vacuum/fsm disregard pages with "uselessly small" amounts of > free space (less than the average tuple size, IIRC). Ah - that what I was seeing! Thanks. > > I do notice a rather serious shortcoming of pg_freespacemap in its > current incarnation, which is that it *only* shows you the per-page free > space data, and not any of the information that would let you determine > what the FSM is doing to filter the raw data. The per-relation > avgRequest and lastPageCount fields would be interesting for instance. > Perhaps there should be a second view with one row per relation to > carry the appropriate data. > Ok - I did wonder about 2 views, but was unsure if the per-relation stuff was interesting. Given that it looks like it is interesting, I'll see about getting a second view going. Cheers Mark
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Re: [PATCHES] pg_freespacemap question
Tatsuo Ishii <ishii@sraoss.co.jp> — 2006-03-13T02:56:37Z
> > Tatsuo Ishii wrote: > >> BTW, I noticed difference of outputs from pg_freespacemap and > >> pgstattuple. > >> > >> I ran pgbench and inspected "accounts" table by using these tools. > >> > >> pg_freespacemap: > >> sum of bytes: 250712 > >> > >> pgstattuple: > >> free_space: 354880 > >> > >> Shouldn't they be identical? > > No, because (a) pgbench vacuums at the start of the run not the end, I ran VACUUM after pbench run and still got the differece. > and (b) vacuum/fsm disregard pages with "uselessly small" amounts of > free space (less than the average tuple size, IIRC). That sounds strange to me. Each record of accounts tables is actually exactly same, i.e fixed size. So it should be possible that UPDATE reuses any free spaces made by previous UPDATE. If FSM neglects those free spaces "because they are uselessly small", then the unrecycled pages are getting grow even if they are regulary VACUUMed, no? > I do notice a rather serious shortcoming of pg_freespacemap in its > current incarnation, which is that it *only* shows you the per-page free > space data, and not any of the information that would let you determine > what the FSM is doing to filter the raw data. The per-relation > avgRequest and lastPageCount fields would be interesting for instance. > Perhaps there should be a second view with one row per relation to > carry the appropriate data. -- Tatsuo Ishii SRA OSS, Inc. Japan
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Re: [PATCHES] pg_freespacemap question
Tom Lane <tgl@sss.pgh.pa.us> — 2006-03-13T03:15:07Z
Tatsuo Ishii <ishii@sraoss.co.jp> writes: > That sounds strange to me. Each record of accounts tables is actually > exactly same, i.e fixed size. So it should be possible that UPDATE > reuses any free spaces made by previous UPDATE. If FSM neglects those > free spaces "because they are uselessly small", then the unrecycled > pages are getting grow even if they are regulary VACUUMed, no? The point here is that if tuples require 50 bytes, and there are 20 bytes free on a page, pgstattuple counts 20 free bytes while FSM ignores the page. Recording that space in the FSM will not improve matters, it'll just risk pushing out FSM records for pages that do have useful amounts of free space. regards, tom lane
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Re: [PATCHES] pg_freespacemap question
Christopher Kings-Lynne <chriskl@familyhealth.com.au> — 2006-03-13T03:29:44Z
> The point here is that if tuples require 50 bytes, and there are 20 > bytes free on a page, pgstattuple counts 20 free bytes while FSM > ignores the page. Recording that space in the FSM will not improve > matters, it'll just risk pushing out FSM records for pages that do > have useful amounts of free space. Maybe an overloaded pgstattuple function that allows you to request FSM behavior? Chris
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Re: [PATCHES] pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-13T04:37:00Z
Christopher Kings-Lynne wrote: >> The point here is that if tuples require 50 bytes, and there are 20 >> bytes free on a page, pgstattuple counts 20 free bytes while FSM >> ignores the page. Recording that space in the FSM will not improve >> matters, it'll just risk pushing out FSM records for pages that do >> have useful amounts of free space. > > > > Maybe an overloaded pgstattuple function that allows you to request FSM > behavior? > That's a nice idea - could also do equivalently by adding an extra column "usable_free_space" or some such, and calculating this using FSM logic. Cheers Mark
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Re: [PATCHES] pg_freespacemap question
Alvaro Herrera <alvherre@commandprompt.com> — 2006-03-13T13:44:12Z
Mark Kirkwood wrote: > Christopher Kings-Lynne wrote: > >>The point here is that if tuples require 50 bytes, and there are 20 > >>bytes free on a page, pgstattuple counts 20 free bytes while FSM > >>ignores the page. Recording that space in the FSM will not improve > >>matters, it'll just risk pushing out FSM records for pages that do > >>have useful amounts of free space. > > > >Maybe an overloaded pgstattuple function that allows you to request FSM > >behavior? > > That's a nice idea - could also do equivalently by adding an extra > column "usable_free_space" or some such, and calculating this using FSM > logic. The current pgstattuple function scans the whole table, so I don't think this is a good idea. Re: the overloaded function, I think the behaviors are different enough to merit a separate function, with a different name. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
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Re: [PATCHES] pg_freespacemap question
Mark Kirkwood <markir@paradise.net.nz> — 2006-03-19T23:33:33Z
Mark Kirkwood wrote: > Tom Lane wrote: > >> >> I do notice a rather serious shortcoming of pg_freespacemap in its >> current incarnation, which is that it *only* shows you the per-page free >> space data, and not any of the information that would let you determine >> what the FSM is doing to filter the raw data. The per-relation >> avgRequest and lastPageCount fields would be interesting for instance. >> Perhaps there should be a second view with one row per relation to >> carry the appropriate data. >> > > Ok - I did wonder about 2 views, but was unsure if the per-relation > stuff was interesting. Given that it looks like it is interesting, I'll > see about getting a second view going. > This patch implements the second view for FSM relations. I have renamed the functions and views to be: pg_freespacemap_relations pg_freespacemap_pages This patch depends on the previous one (which was called simply 'pg_freespacemap.patch'). Cheers Mark
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Re: [HACKERS] pg_freespacemap question
Bruce Momjian <pgman@candle.pha.pa.us> — 2006-04-26T22:41:25Z
Patch applied. Thanks. --------------------------------------------------------------------------- Mark Kirkwood wrote: > Tom Lane wrote: > > Mark Kirkwood <markir@paradise.net.nz> writes: > > > >>>Good points! I had not noticed this test case. Probably NULL is better > > > > > >>Would setting it to 'BLCKSZ - (fixed index header stuff)' be better, > > > > > > No, I don't think so, because that will just make it harder to recognize > > what's what (remember that BLCKSZ isn't really a constant, and the index > > overhead is not the same for all AMs either). The point here is that > > for indexes the FSM tracks whole-page availability, not the amount of > > free space within pages. So I think NULL is a reasonable representation > > of that. Using NULL will make it easy to filter the results if you want > > to see only heap-page data or only index-page data, whereas it will be > > very hard to do that if the view adopts an ultimately-artificial > > convention about the amount of available space on an index page. > > > > Right - after suggesting it I realized that coding the different index > overhead for each possible AM would have been ... difficult :-). A patch > is attached to implement the NULL free bytes and other recommendations: > > 1/ Index free bytes set to NULL > 2/ Comment added to the README briefly mentioning the index business > 3/ Columns reordered more logically > 4/ 'Blockid' column removed > 5/ Free bytes column renamed to just 'bytes' instead of 'blockfreebytes' > > Now 5/ was only hinted at, but seemed worth doing while I was there > (hopefully I haven't made it too terse now....). > > cheers > > Mark > > > Index: pg_freespacemap.c > =================================================================== > RCS file: /projects/cvsroot/pgsql/contrib/pg_freespacemap/pg_freespacemap.c,v > retrieving revision 1.2 > diff -c -r1.2 pg_freespacemap.c > *** pg_freespacemap.c 14 Feb 2006 15:03:59 -0000 1.2 > --- pg_freespacemap.c 9 Mar 2006 03:38:10 -0000 > *************** > *** 12,18 **** > #include "storage/freespace.h" > #include "utils/relcache.h" > > ! #define NUM_FREESPACE_PAGES_ELEM 6 > > #if defined(WIN32) || defined(__CYGWIN__) > /* Need DLLIMPORT for some things that are not so marked in main headers */ > --- 12,18 ---- > #include "storage/freespace.h" > #include "utils/relcache.h" > > ! #define NUM_FREESPACE_PAGES_ELEM 5 > > #if defined(WIN32) || defined(__CYGWIN__) > /* Need DLLIMPORT for some things that are not so marked in main headers */ > *************** > *** 29,40 **** > typedef struct > { > > - uint32 blockid; > - uint32 relfilenode; > uint32 reltablespace; > uint32 reldatabase; > uint32 relblocknumber; > ! uint32 blockfreebytes; > > } FreeSpacePagesRec; > > --- 29,40 ---- > typedef struct > { > > uint32 reltablespace; > uint32 reldatabase; > + uint32 relfilenode; > uint32 relblocknumber; > ! uint32 bytes; > ! bool isindex; > > } FreeSpacePagesRec; > > *************** > *** 91,107 **** > > /* Construct a tuple to return. */ > tupledesc = CreateTemplateTupleDesc(NUM_FREESPACE_PAGES_ELEM, false); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 1, "blockid", > ! INT4OID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 2, "relfilenode", > OIDOID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 3, "reltablespace", > OIDOID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 4, "reldatabase", > OIDOID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 5, "relblocknumber", > INT8OID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 6, "blockfreebytes", > INT4OID, -1, 0); > > /* Generate attribute metadata needed later to produce tuples */ > --- 91,105 ---- > > /* Construct a tuple to return. */ > tupledesc = CreateTemplateTupleDesc(NUM_FREESPACE_PAGES_ELEM, false); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 1, "reltablespace", > OIDOID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 2, "reldatabase", > OIDOID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 3, "relfilenode", > OIDOID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 4, "relblocknumber", > INT8OID, -1, 0); > ! TupleDescInitEntry(tupledesc, (AttrNumber) 5, "bytes", > INT4OID, -1, 0); > > /* Generate attribute metadata needed later to produce tuples */ > *************** > *** 129,135 **** > fctx->values[2] = (char *) palloc(3 * sizeof(uint32) + 1); > fctx->values[3] = (char *) palloc(3 * sizeof(uint32) + 1); > fctx->values[4] = (char *) palloc(3 * sizeof(uint32) + 1); > - fctx->values[5] = (char *) palloc(3 * sizeof(uint32) + 1); > > > /* Return to original context when allocating transient memory */ > --- 127,132 ---- > *************** > *** 158,169 **** > for (nPages = 0; nPages < fsmrel->storedPages; nPages++) > { > > - fctx->record[i].blockid = i; > - fctx->record[i].relfilenode = fsmrel->key.relNode; > fctx->record[i].reltablespace = fsmrel->key.spcNode; > fctx->record[i].reldatabase = fsmrel->key.dbNode; > fctx->record[i].relblocknumber = IndexFSMPageGetPageNum(page); > ! fctx->record[i].blockfreebytes = 0; /* index.*/ > > page++; > i++; > --- 155,166 ---- > for (nPages = 0; nPages < fsmrel->storedPages; nPages++) > { > > fctx->record[i].reltablespace = fsmrel->key.spcNode; > fctx->record[i].reldatabase = fsmrel->key.dbNode; > + fctx->record[i].relfilenode = fsmrel->key.relNode; > fctx->record[i].relblocknumber = IndexFSMPageGetPageNum(page); > ! fctx->record[i].bytes = 0; > ! fctx->record[i].isindex = true; > > page++; > i++; > *************** > *** 178,189 **** > > for (nPages = 0; nPages < fsmrel->storedPages; nPages++) > { > - fctx->record[i].blockid = i; > - fctx->record[i].relfilenode = fsmrel->key.relNode; > fctx->record[i].reltablespace = fsmrel->key.spcNode; > fctx->record[i].reldatabase = fsmrel->key.dbNode; > fctx->record[i].relblocknumber = FSMPageGetPageNum(page); > ! fctx->record[i].blockfreebytes = FSMPageGetSpace(page); > > page++; > i++; > --- 175,186 ---- > > for (nPages = 0; nPages < fsmrel->storedPages; nPages++) > { > fctx->record[i].reltablespace = fsmrel->key.spcNode; > fctx->record[i].reldatabase = fsmrel->key.dbNode; > + fctx->record[i].relfilenode = fsmrel->key.relNode; > fctx->record[i].relblocknumber = FSMPageGetPageNum(page); > ! fctx->record[i].bytes = FSMPageGetSpace(page); > ! fctx->record[i].isindex = false; > > page++; > i++; > *************** > *** 209,227 **** > if (funcctx->call_cntr < funcctx->max_calls) > { > uint32 i = funcctx->call_cntr; > > > - sprintf(fctx->values[0], "%u", fctx->record[i].blockid); > - sprintf(fctx->values[1], "%u", fctx->record[i].relfilenode); > - sprintf(fctx->values[2], "%u", fctx->record[i].reltablespace); > - sprintf(fctx->values[3], "%u", fctx->record[i].reldatabase); > - sprintf(fctx->values[4], "%u", fctx->record[i].relblocknumber); > - sprintf(fctx->values[5], "%u", fctx->record[i].blockfreebytes); > > > > /* Build and return the tuple. */ > ! tuple = BuildTupleFromCStrings(funcctx->attinmeta, fctx->values); > result = HeapTupleGetDatum(tuple); > > > --- 206,246 ---- > if (funcctx->call_cntr < funcctx->max_calls) > { > uint32 i = funcctx->call_cntr; > + char *values[NUM_FREESPACE_PAGES_ELEM]; > + int j; > > + /* > + * Use a temporary values array, initially pointing to fctx->values, > + * so it can be reassigned w/o losing the storage for subsequent > + * calls. > + */ > + for (j = 0; j < NUM_FREESPACE_PAGES_ELEM; j++) > + { > + values[j] = fctx->values[j]; > + } > + > + > + sprintf(values[0], "%u", fctx->record[i].reltablespace); > + sprintf(values[1], "%u", fctx->record[i].reldatabase); > + sprintf(values[2], "%u", fctx->record[i].relfilenode); > + sprintf(values[3], "%u", fctx->record[i].relblocknumber); > > > + /* > + * Set (free) bytes to NULL for an index relation. > + */ > + if (fctx->record[i].isindex == true) > + { > + values[4] = NULL; > + } > + else > + { > + sprintf(values[4], "%u", fctx->record[i].bytes); > + } > > > /* Build and return the tuple. */ > ! tuple = BuildTupleFromCStrings(funcctx->attinmeta, values); > result = HeapTupleGetDatum(tuple); > > > Index: pg_freespacemap.sql.in > =================================================================== > RCS file: /projects/cvsroot/pgsql/contrib/pg_freespacemap/pg_freespacemap.sql.in,v > retrieving revision 1.2 > diff -c -r1.2 pg_freespacemap.sql.in > *** pg_freespacemap.sql.in 27 Feb 2006 16:09:48 -0000 1.2 > --- pg_freespacemap.sql.in 9 Mar 2006 03:42:15 -0000 > *************** > *** 11,17 **** > -- Create a view for convenient access. > CREATE VIEW pg_freespacemap AS > SELECT P.* FROM pg_freespacemap() AS P > ! (blockid int4, relfilenode oid, reltablespace oid, reldatabase oid, relblocknumber int8, blockfreebytes int4); > > -- Don't want these to be available at public. > REVOKE ALL ON FUNCTION pg_freespacemap() FROM PUBLIC; > --- 11,17 ---- > -- Create a view for convenient access. > CREATE VIEW pg_freespacemap AS > SELECT P.* FROM pg_freespacemap() AS P > ! (reltablespace oid, reldatabase oid, relfilenode oid, relblocknumber int8, bytes int4); > > -- Don't want these to be available at public. > REVOKE ALL ON FUNCTION pg_freespacemap() FROM PUBLIC; > Index: README.pg_freespacemap > =================================================================== > RCS file: /projects/cvsroot/pgsql/contrib/pg_freespacemap/README.pg_freespacemap,v > retrieving revision 1.1 > diff -c -r1.1 README.pg_freespacemap > *** README.pg_freespacemap 12 Feb 2006 03:55:53 -0000 1.1 > --- README.pg_freespacemap 9 Mar 2006 03:43:16 -0000 > *************** > *** 34,45 **** > > Column | references | Description > ----------------+----------------------+------------------------------------ > - blockid | | Id, 1.. max_fsm_pages > - relfilenode | pg_class.relfilenode | Refilenode of the relation. > reltablespace | pg_tablespace.oid | Tablespace oid of the relation. > reldatabase | pg_database.oid | Database for the relation. > relblocknumber | | Offset of the page in the relation. > ! blockfreebytes | | Free bytes in the block/page. > > > There is one row for each page in the free space map. > --- 34,45 ---- > > Column | references | Description > ----------------+----------------------+------------------------------------ > reltablespace | pg_tablespace.oid | Tablespace oid of the relation. > reldatabase | pg_database.oid | Database for the relation. > + relfilenode | pg_class.relfilenode | Refilenode of the relation. > relblocknumber | | Offset of the page in the relation. > ! bytes | | Free bytes in the block/page, or NULL > ! | | for an index page (see below). > > > There is one row for each page in the free space map. > *************** > *** 47,52 **** > --- 47,55 ---- > Because the map is shared by all the databases, there are pages from > relations not belonging to the current database. > > + The free space map can contain pages for btree indexes if they were emptied > + by a vacuum process. The bytes field is set to NULL in this case. > + > When the pg_freespacemap view is accessed, internal free space map locks are > taken, and a copy of the map data is made for the view to display. > This ensures that the view produces a consistent set of results, while not > *************** > *** 58,91 **** > ------------- > > regression=# \d pg_freespacemap > ! View "public.pg_freespacemap" > Column | Type | Modifiers > ! ---------------+---------+----------- > ! blockid | integer | > ! relfilenode | oid | > reltablespace | oid | > reldatabase | oid | > relblocknumber | bigint | > ! blockfreebytes | integer | > View definition: > ! SELECT p.blockid, p.relfilenode, p.reltablespace, p.reldatabase, p.relblocknumber, p.blockfreebytes > ! FROM pg_freespacemap() p(blockid integer, relfilenode oid, reltablespace oid, reldatabase oid, relblocknumber bigint, blockfreebytes integer); > > ! regression=# SELECT c.relname, m.relblocknumber, m.blockfreebytes > FROM pg_freespacemap m INNER JOIN pg_class c > ON c.relfilenode = m.relfilenode LIMIT 10; > ! relname | relblocknumber | blockfreebytes > ! ------------------------+----------------+---------------- > ! sql_features | 5 | 2696 > ! sql_implementation_info | 0 | 7104 > ! sql_languages | 0 | 8016 > ! sql_packages | 0 | 7376 > ! sql_sizing | 0 | 6032 > ! pg_authid | 0 | 7424 > ! pg_toast_2618 | 13 | 4588 > ! pg_toast_2618 | 12 | 1680 > ! pg_toast_2618 | 10 | 1436 > ! pg_toast_2618 | 7 | 1136 > (10 rows) > > regression=# > --- 61,93 ---- > ------------- > > regression=# \d pg_freespacemap > ! View "public.pg_freespacemap" > Column | Type | Modifiers > ! ----------------+---------+----------- > reltablespace | oid | > reldatabase | oid | > + relfilenode | oid | > relblocknumber | bigint | > ! bytes | integer | > View definition: > ! SELECT p.reltablespace, p.reldatabase, p.relfilenode, p.relblocknumber, p.bytes > ! FROM pg_freespacemap() p(reltablespace oid, reldatabase oid, relfilenode oid, relblocknumber bigint, bytes integer); > > ! regression=# SELECT c.relname, m.relblocknumber, m.bytes > FROM pg_freespacemap m INNER JOIN pg_class c > ON c.relfilenode = m.relfilenode LIMIT 10; > ! relname | relblocknumber | bytes > ! ------------------------+----------------+-------- > ! sql_features | 5 | 2696 > ! sql_implementation_info | 0 | 7104 > ! sql_languages | 0 | 8016 > ! sql_packages | 0 | 7376 > ! sql_sizing | 0 | 6032 > ! pg_authid | 0 | 7424 > ! pg_toast_2618 | 13 | 4588 > ! pg_toast_2618 | 12 | 1680 > ! pg_toast_2618 | 10 | 1436 > ! pg_toast_2618 | 7 | 1136 > (10 rows) > > regression=# > > > > ---------------------------(end of broadcast)--------------------------- > TIP 9: In versions below 8.0, the planner will ignore your desire to > choose an index scan if your joining column's datatypes do not > match -- Bruce Momjian http://candle.pha.pa.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + -
Re: [HACKERS] pg_freespacemap question
Bruce Momjian <pgman@candle.pha.pa.us> — 2006-04-26T22:46:18Z
Patch applied. Thanks. --------------------------------------------------------------------------- Mark Kirkwood wrote: > Mark Kirkwood wrote: > > Tom Lane wrote: > > > >> > >> I do notice a rather serious shortcoming of pg_freespacemap in its > >> current incarnation, which is that it *only* shows you the per-page free > >> space data, and not any of the information that would let you determine > >> what the FSM is doing to filter the raw data. The per-relation > >> avgRequest and lastPageCount fields would be interesting for instance. > >> Perhaps there should be a second view with one row per relation to > >> carry the appropriate data. > >> > > > > Ok - I did wonder about 2 views, but was unsure if the per-relation > > stuff was interesting. Given that it looks like it is interesting, I'll > > see about getting a second view going. > > > > This patch implements the second view for FSM relations. I have renamed > the functions and views to be: > > pg_freespacemap_relations > pg_freespacemap_pages > > This patch depends on the previous one (which was called simply > 'pg_freespacemap.patch'). > > Cheers > > Mark [ application/gzip is not supported, skipping... ] > > ---------------------------(end of broadcast)--------------------------- > TIP 4: Have you searched our list archives? > > http://archives.postgresql.org -- Bruce Momjian http://candle.pha.pa.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. +